Defendant, Harold Miller, who pleaded guilty to conspiring to distribute 1.25 ounces of cocaine hydrochloride in violation of 21 U.S.C. §§ 841 and 846, appeals the 60-month sentence imposed upon him under the Sentencing Guidelines. Specifically, the defendant argues that his waiver of the right to counsel was defective, and that statements he made to his probation officer should not have been used to establish the amount of cocaine that he distributed. In addition, the defendant challenges the district court’s inclusion of drug sales outside the period of the conspiracy as relevant conduct, and further contends that the district court incorrectly enhanced his guideline sentence based upon the erroneous determination that he possessed a firearm during the commission of a drug offense. Finding no merit in any of these arguments, we affirm.
I.
An investigation of defendant Miller that began in March of 1988 resulted in three separate sales of cocaine hydrochloride by the defendant to an undercover informant. On each occasion, the informant wore a recording device, thereby generating a tape of each transaction. The investigation culminated in the arrest of defendant Miller on October 24, 1988. On the date of his arrest, the defendant, acting in a pro se capacity after being advised of his rights and waiving his right to counsel, arranged a plea agreement with the government that required the defendant to forgo his right to an indictment and plead guilty to conspiring to distribute 1.25 ounces of cocaine between March 1, 1988, and May 11, 1988. The defendant also consented to furnish truthful testimony for the government and serve as an undercover informant upon request.1 In exchange, the government promised not to prosecute Miller further for cocaine distribution so long as he “abide[d] by the terms of th[e] agreement.”
On March 17, 1989, the defendant appeared before the district court, signed a waiver of counsel form, and entered a guilty plea to a single-count information charging him with conspiring to distribute 1.25 ounces of cocaine hydrochloride “between March 1, 1988, and May 11, 1988[.]” Before accepting the defendant’s plea, the district judge engaged in a colloquy with the defendant to ascertain whether the defendant understood his right to counsel and the perils of proceeding pro se. The district judge explained the charge, the potential penalties, and the fact that the Sentencing Guidelines would dictate the range of *1323the resulting sentence. After the defendant expressed his desire to proceed in his own defense, the district court explicitly found “that the defendant has knowingly and voluntarily waived his right to counsel.” The waiver of counsel form signed by the defendant at that point in the proceedings memorialized the defendant’s stated intention.
Once the defendant had waived his right to counsel, the district court proceeded to advise the defendant of his rights and take his guilty plea. Defendant Miller personally acknowledged the various rights enumerated by the district court, signed a form waiving his right to have the case submitted to the grand jury, and formally adopted the government’s explanation of the conduct supporting the charge. The plea proceeding ended with the following comments from the district court:
THE COURT: Mr. Winck will explain that to you and tell you where you need to go to see the probation officer. Now, that person is very helpful, Mr. Miller. He or she, as the ease may be, is an officer of this Court and they’ll be getting all the information from you concerning your past, what your problem was with this crime, and they’ll submit that report to me and then I’ll review that and use that, in part, in determining what sentence should be imposed. So be honest and candid with the probation officer, okay?
A. Yes, sir.
THE COURT: Because you will be working with that person for a long time and, as I say, those people can help you.
A: Yes, sir.
During a meeting with his probation officer, defendant Miller revealed that he had purchased approximately one ounce of cocaine per week between February 1987 and October 1988. The defendant further explained to his probation officer that he typically used half of the cocaine that he bought, and sold the other half to support his habit. Proceeding from this disclosure, the probation officer calculated that the defendant had sold 1,169.5 grams of cocaine over a 20-month period. Accordingly, the probation officer used the 1,169.5 gram figure, rather than the 35.5 gram (1.25 ounce) figure charged in the information, to establish the base offense level in the defendant’s presentence report. The impact of the 1,169.5 gram figure as reflected in the presentence report was substantial. Application of the 1,169.5 gram figure resulted in a base offense level of 26, see U.S.S.G. § 2D1.1(c)(9), which yielded a sentencing range of 63 to 78 months, see id. Ch. 5, Pt. A (Sentencing Table), whereas the 35.5 gram figure would have produced a base offense level of 14, see id. § 2Dl.l(c)(15), and a sentencing range of 15 to 21 months. See id. Ch. 5, Pt. A (Sentencing Table). Upon learning of the probation officer’s proposed sentencing range, the defendant sought and obtained appointed counsel to prepare for the sentencing hearing.
After counsel was appointed, the defendant filed a motion to disallow the use of information revealed to the probation officer in the calculation of the appropriate guideline sentence. The district court denied the motion as well as the defendant’s subsequent motion for reconsideration. On August 8,1989, the district court conducted a sentencing hearing. At the outset of the hearing, the defendant indicated through counsel that he affirmatively “elected to go forward with the plea under the information.” The government then presented evidence that defendant Miller had engaged in at least one sale of cocaine with a pistol readily accessible on a nearby table. The defendant admitted ownership and possession of various guns, but argued that no weapon was present when any sale of cocaine occurred. The district court, characterizing the defendant’s weekly cocaine sales revealed to the probation officer as “relevant conduct,” see U.S.S.G. § 1B1.3, set the base offense level at 26. The court then added two points to the base offense level for possession of a weapon during the commission of the offense, see id. § 2D1.1(b)(1), and deducted two points for the defendant’s acceptance of responsibility. See id. § 3E1.1. Arriving at a sentencing range of 63 to 78 months, the district court, sua sponte, departed downward to a *132460-month sentence because there were “not any real aggravating factors in this case.”
The defendant filed a timely notice of appeal; the government did not cross-appeal.2 The defendant raises four assignments of error for our consideration. First, he alleges that the district court failed to obtain an effective waiver of his right to counsel. Second, he contends that his statements made to his probation officer cannot provide the basis for establishing his base offense level. Third, he asserts that the district court improperly characterized the information he provided to the probation officer as “relevant conduct” in setting his base offense level at 26. Finally, he argues that the district court erred in finding that he used a firearm in the course of committing the offense of conviction. We shall address these issues seriatim.
II.
The Supreme Court's decision in Faretta v. California, 422 U.S. 806, 95 S.Ct. 2525, 45 L.Ed.2d 562 (1975), clearly established that the sixth amendment “grants to the accused personally the right to make his defense” through self-representation. Id. at 819, 95 S.Ct. at 2533. Self-representation, however, must be undertaken only upon a showing “that an accused was offered counsel but intelligently and understandingly rejected the offer.” Carnley v. Cochran, 369 U.S. 506, 516, 82 S.Ct. 884, 890, 8 L.Ed.2d 70 (1962); accord United States v. Grosshans, 821 F.2d 1247, 1250 (6th Cir.), cert. denied, 484 U.S. 987, 108 S.Ct. 506, 98 L.Ed.2d 505 (1987); see also Faretta, 422 U.S. at 835, 95 S.Ct. at 2541. We have recognized the difficulties that district courts face when confronted with defendants who wish to waive their right to counsel, see United States v. McDowell, 814 F.2d 245, 248-49 (6th Cir.), cert. denied, 484 U.S. 980, 108 S.Ct. 478, 98 L.Ed.2d 492 (1987), and have “invoke[d] our supervisory powers to identify the nature of the inquiry to be made and the procedure to be followed ... in situations where an accused seeks to waive representation by counsel and proceed pro se.” Id. at 250. Specifically, we adopted the “model inquiry ... set forth in 1 Bench Book for United States District Judges 1.02-2 (3d ed. 1986)[,]” McDowell, 814 F.2d at 250, mandated adherence to “the model inquiry or one covering the same substantive points,” id., and required a finding on the record of informed insistence upon self-representation as preconditions to a valid waiver of the right to counsel. See id.
In this case, we find that the district court substantially complied with the model inquiry adopted in McDowell, 814 F.2d at 250, and that the defendant therefore effectively waived his right to counsel. See id. at 252 (Engel, J., concurring) (“[T]he rule today, based upon our supervisory powers, requires substantial compliance and not literal adherence to the guidelines in the Bench Book.”). The model inquiry, which is set forth as an appendix to the McDowell opinion, see id. at 251-52, prescribes a battery of questions designed to ascertain the defendant’s familiarity with the law, to warn the defendant of the gravity of the charges and the dangers of self-representation, and to determine whether the defendant’s decision to waive counsel is voluntary. Here, the district court’s searching inquiry touched upon all of the relevant considerations addressed by the model inquiry.3 Accordingly, we find no merit in the defendant’s contention that he did not *1325effectively forsake his right to counsel before pleading guilty to the charge set forth in the single-count information.
Even assuming arguendo that the defendant did not effectively waive his right to counsel, his ratification of the plea agreement after he obtained appointed counsel supports his conviction under the plea agreement’s terms. At the sentencing hearing, counsel for the defendant expressly stated that “[i]n my file there is a motion to withdraw the plea. Mr. Miller has asked that I not file that motion, but instead allow the court to go ahead with these proceedings.” Similarly, in United States v. Billington, 844 F.2d 445 (7th Cir.1988), “the defendant not only ratified his initial guilty plea, but unequivocally refused to withdraw his plea of guilty [when] the court allowed him to reconsider his plea.” Id. at 450. Here, as in Billington, the defendant’s dissatisfaction with the sentence imposed under the plea agreement does not give rise to a viable claim of constitutional dimension. Defendant Miller’s decision to abide by the terms of his plea agreement after he obtained counsel constitutes a waiver of any sixth amendment violation that may have preceded the appointment of counsel.
III.
Defendant Miller challenges the district court’s authority to consider statements he made to his probation officer on two grounds. First, he contends that Sentencing Guideline § lB1.8(a) prohibits the use of such information for purposes of establishing the applicable guideline range. We disagree. According to section 1B1.-8(a):
Where a defendant agrees to cooperate with the government by providing information concerning unlawful activities of others, and the government agrees that self-incriminating information so provided will not be used against the defendant, then such information shall not be used in determining the applicable guideline range, except to the extent provided in the agreement.
U.S.S.G. § lB1.8(a). This section unquestionably forbids the government to influence the sentencing range by disclosing revelations made by a defendant in the course of cooperation as required by a plea agreement. See, e.g., United States v. Shorteeth, 887 F.2d 253, 255-57 (10th Cir.1989); U.S.S.G. § 1B1.8, comment, (n. 1). Statements made to a probation officer, however, cannot be construed as information provided to the “government” within the meaning of section lB1.8(a). Cf. United States v. Perez-Franco, 873 F.2d 455, 460-61 (1st Cir.1989) (Federal Rule of Evidence 410, which excludes “any statement *1326made in the course of plea discussions with an attorney for the prosecuting authority,” does not bar “statements made to a probation officer in preparation for a presen-tence report_”). As the Ninth Circuit recently explained, probation officers under the guideline system still operate on behalf of the court, not the prosecutorial arm of the government contemplated by section lB1.8(a).4 See United States v. Belgard, 894 F.2d 1092, 1096-97 (9th Cir.1990).
The defendant’s second argument concerning statements made to the probation officer refers to the fifth amendment’s protection against self-incrimination and invites this court to formulate prophylactic warnings presumably under our supervisory authority. Insofar as the defendant seeks redress for violation of his fifth amendment rights, the Supreme Court’s decision in Minnesota v. Murphy, 465 U.S. 420, 104 S.Ct. 1136, 79 L.Ed.2d 409 (1984), precludes the relief that he has requested. Under Murphy, the fifth amendment privilege against self-incrimination is not self-executing in the context of a meeting with a probation officer. See id. at 425, 104 S.Ct. at 1141. Consequently, “since [defendant Miller] revealed incriminating information instead of timely asserting his Fifth Amendment privilege, his disclosures were not compelled incriminations.” Id. at 440, 104 S.Ct. at 1149. We likewise reject the defendant’s suggestion that the guideline sentencing scheme warrants the creation of Miranda-type5 prophylactic warnings to be administered prior to presentence meetings with probation officers. In Baumann v. United States, 692 F.2d 565 (9th Cir.1982), the Ninth Circuit observed that “Miranda has never been applied, to our knowledge, to routine presentence interviews conducted for the benefit of a district judge in the exercise of his substantial discretion at sentencing. We see no reason to do so.” Id. at 576. Defendant Miller claims that, with the advent of guideline sentencing and the concomitant restriction of district judges’ sentencing discretion, the rationale supporting the Ninth Circuit’s refusal to extend Miranda uniformly to pre-sentence interviews has been undercut. We disagree. Under the guideline sentencing scheme, the district court must resolve factual disputes and, in doing so, remains at liberty to disregard information and recommendations included in the presentence report compiled by the probation officer. See, e.g., Belgard, 894 F.2d at 1097, 1099. We therefore find the pre-guideline logic of Baumann relevant to guideline sentencing. Accord United States v. Rogers, 899 F.2d 917, 921-24 (10th Cir.1990).
IV.
The defendant’s principal challenge to the district court’s application of the guidelines focuses on the district court’s conceptualization of “relevant conduct,” which is discussed extensively in Sentencing Guideline § 1B1.3. Pursuant to section lB1.3(a)(2), the base offense level “shall be determined on the basis of ... all such acts and omissions that were part of the same course of conduct or common scheme or plan as the offense of conviction ... solely with respect to offenses of a character for which § 3D1.2(d) would require grouping of multiple counts[.]” 6 See U.S.S.G. § lB1.3(a)(2) (emphasis added). The commentary accompanying section 1B1.3 states that, “in a drug distribution case, quantities and types of drugs not specified in the count of conviction are to be included in determining the offense level if they were part of the same course of *1327conduct or part of a common scheme or plan as the count of conviction.” U.S.S.G. § 1B1.3, comment, (backg’d). Relying upon this language, the district court aggregated the total amount of cocaine admittedly sold by the defendant over a 20-month period to arrive at a base offense level of 26. The defendant asserts that the district court was constrained to rely upon the 35.5 gram and the three-month conspiracy figures charged in the count of conviction.
Our decision in United States v. Sailes, 872 F.2d 735 (6th Cir.1989), illustrates that, pursuant to section lB1.3(a)(2), the entire quantity of cocaine attributable to a distribution enterprise must be used to establish the base offense level of a conspirator in the undertaking. See id. at 738-39. Indeed, in United States v. Smith, 887 F.2d 104 (6th Cir.1989), we determined that conduct charged in a count that was dismissed in accordance with a plea agreement should be considered in establishing the base offense level if such conduct related to the offense of conviction. See id. at 107-08. In the process of reaching this conclusion, we observed that consideration of “conduct for which the defendant was not convicted is consistent with preguidelines practice.” Id. at 108 n. 5.
We addressed the impact of uncharged conduct, which is at issue here, in United States v. Silverman, 889 F.2d 1531 (6th Cir.1989), but resolved the case without direct reference to the “relevant conduct” provision of the guidelines. See id. at 1539. Instead, we refused to include uncharged conduct in the base offense level calculation because the defendant’s plea agreement prohibited the government from “fil[ing] ‘additional charges’ ” against the defendant. See id. We deduced that “[t]he effect of the findings by the district court may have been, at least indirectly, to take into account ‘additional charges,’ if not brought formally by the United States Attorney then by the probation office or the law enforcement agents involved in the sentencing process.” Id. In short, we viewed the inclusion of uncharged conduct in the total controlled substance figure used to set the base offense level as inconsistent with the terms of the defendant’s plea agreement barring “additional charges.”
Defendant Miller’s plea agreement similarly guaranteed no further prosecution, but the government’s promise to this effect was predicated upon the defendant’s compliance with the terms of his plea agreement. Because both the defendant and the government agree that the defendant failed to fulfill his obligations under the plea agreement, the concern addressed in Sil-verman is not implicated here. Thus, we must deal directly with the question of whether uncharged conduct related to the offense of conviction can form the basis for the base offense level. The district court held that Sentencing Guideline § 1B1.3(a)(2) requires consideration of uncharged relevant conduct, and we agree. See, e.g., United States v. Frederick, 897 F.2d 490 (10th Cir.1990); United States v. Mocciola, 891 F.2d 13, 16 (1st Cir.1989); United States v. Allen, 886 F.2d 143, 145 (8th Cir.1989); see also United States v. Vopravil, 891 F.2d 155, 157 (7th Cir.1989); but see United States v. Restrepo, 883 F.2d 781, 786 (9th Cir.1989).7 As the First Circuit explained, “whether uncharged drugs are part of a common scheme or plan is a factual finding we will disturb only if clearly erroneous.” Mocciola, 891 F.2d at 16. In this case, we cannot say that the district court’s inclusion of cocaine sold over a 20-month period as conduct related to the offense of conviction was clearly erroneous. Accordingly, we find no justification for modifying the defendant’s sentence based upon the district court’s treatment of relevant conduct.8
*1328V.
The defendant’s final assignment of error relates to the two-level enhancement imposed by the district court for possession of a weapon during the offense of conviction. Sentencing Guideline § 2D1.1(b)(1) provides that “[i]f a dangerous weapon (including a firearm) was possessed during commission of the offense, increase by 2 levels.” Defendant Miller asserts that the government presented insufficient evidence at the sentencing hearing to establish the presence of a weapon during any of the three drug transactions between the defendant and the informant. In this respect, it is clear that “[t]he preponderance of the evidence standard applies to contested facts in sentencing proceedings.” Silverman, 889 F.2d at 1535. “The government bears the burden to establish enhancement factors, where contested.”9 Id.; see also United States v. Rodriguez, 896 F.2d 1031, 1032 (6th Cir.1990).
The government introduced hearsay testimony of agent Scott Nowinski concerning the informant’s observation of a gun on a nearby table during the course of one drug sale by the defendant to the informant. Sentencing Guideline § 6A1.3 provides that, “[i]n resolving any reasonable dispute concerning a factor important to the sentencing determination, the [district] court may consider relevant information without regard to its admissibility under the rules of evidence applicable at trial, provided that the information has sufficient indicia of reliability to support its probable accuracy.” Moreover, as the Fifth Circuit recently noted, “the commentary to guideline section 6A1.3 specifically permits consideration of testimony at sentencing hearings that would not be admissible at trial.” United States v. Cuellar-Flores, 891 F.2d 92, 93 (5th Cir.1989). Thus, the hearsay testimony of the agent in this case was properly admitted at the sentencing hearing. See, e.g., United States v. Sciarrino, 884 F.2d 95, 97 (3d Cir.), cert. denied, — U.S. -, 110 S.Ct. 553, 107 L.Ed.2d 549 (1989); Cuellar-Flores, 891 F.2d at 93; see also United States v. Fox, 889 F.2d 357, 360 (1st Cir.1989). Agent Nowinski’s testimony regarding the presence of the firearm was corroborated by the defendant’s admission that he kept guns in the house, although the defendant disputed the assertion that a gun was present during any of the sales to the informant. Significantly, the commentary to section 2D1.1 states:
The enhancement for weapon possession reflects the increased danger of violence when drug traffickers possess weapons. The [two-level] adjustment should be applied if the weapon was present, unless it is clearly improbable that the weapon was connected with the offense....
U.S.S.G. § 2D1.1, comment, (n. 3). The Eighth Circuit has upheld a two-level enhancement under section 2D1.1(b)(2) based only on “undenied possession of a firearm and ammunition in the same place where [the defendant] conducted drug transactions,” see United States v. Green, 889 F.2d 187, 189 (8th Cir.1989), and we similarly have affirmed such a finding. See United States v. McGhee, 882 F.2d 1095, 1099 (6th Cir.1989). We review the district court’s factual finding that the defendant possessed a firearm during the commission of the offense of conviction only for clear error, see Green, 889 F.2d at 188 (citing 18 U.S.C. § 3742(e)); see also United States v. Perez, 871 F.2d 45, 47-48 (6th Cir.), cert. denied, — U.S.-, 109 S.Ct. 3227, 106 L.Ed.2d 576 (1989), and we find that the district court’s determination was not clearly erroneous.
AFFIRMED.
. By all accounts, the defendant failed to satisfy this obligation. Nevertheless, neither party sought to rescind the plea agreement based on the defendant’s lack of cooperation.
. The government’s failure to appeal precludes us from reviewing the district court’s decision to depart downward from the 63 to 78-month guideline range. Cf. 18 U.S.C. § 3742(b) ("The Government, with the personal approval of the Attorney General or Solicitor General, may file a notice of appeal in the district court for review of an otherwise final sentence!.]” (emphasis added)). We note in passing, however, that the district court's stated rationale for departure does not appear to comport with the standard set forth in 18 U.S.C. § 3553(b). See, e.g., United States v. Aguilar-Pena, 887 F.2d 347, 349 (1st Cir.1989) ("Departure is permitted in those cases where idiosyncratic circumstances warrant individualization of sentence beyond that which is possible within the comparatively close-hewn parameters constructed by the guidelines.”).
. The discussion between the district court and the defendant proceeded as follows:
THE COURT: It’s the understanding of this Court that you wish to proceed without an attorney in this matter; is that correct, sir?
*1325A: Yes, sir.
THE COURT: You understand that you have a right to have an attorney to represent you and that if you cannot financially afford an attorney, the Court will appoint an attorney for you and it won’t cost you anything?
A: Yes, sir, I understand that, your Honor.
THE COURT: Do you want me to do that?
A: No, sir.
THE COURT: Have you ever represented yourself in any other matter?
A: No, sir.
THE COURT: In any other criminal action?
A: No, sir.
THE COURT: You realize, sir, that you are charged with conspiracy to distribute cocaine, as set out in this single count of the Information and you realize that if you plead guilty to this charge the Court may impose an assessment of $50.00 and could sentence you to as many as 20 years in prison and fine you as much as one million dollars; do you understand that?
A: Yes, your Honor.
THE COURT: And you realize the United States Sentencing Commission has issued sentencing guidelines that will affect your sentence if you plead guilty?
A: Yes, your Honor.
THE COURT: In light of the penalty involved that you might suffer if you plead guilty and in light of all the difficulties of representing yourself, is it still your desire to represent yourself and to give up your right to be represented by a lawyer?
A: Yes, your Honor.
THE COURT: Is your decision entirely voluntary on your part?
A: Yes, sir, it was, your Honor.
THE COURT: The Court finds that the defendant has knowingly and voluntarily waived his right to counsel. I will, therefore, permit him to represent himself.
.Our determination that the term "government” as employed in section IB 1.8(a) does not include probation officers obviates the need to consider the effect, if any, of the defendant’s failure to provide the cooperation promised in his plea agreement. See U.S.S.G. § lB1.8(b)(3) ("The provisions of subsection (a) shall not be applied to restrict the use of information in the event there is a breach of the cooperation agreement.”).
. Miranda v. Arizona, 384 U.S. 436, 86 S.Ct. 1602, 16 L.Ed.2d 694 (1966).
. Sentencing Guideline § 3D1.2(d), which deals with grouping of closely-related counts, requires grouping of counts "if the offense level is determined largely on the basis of ... the quantity of a substance involved[.]” Distribution of a controlled substance such as cocaine falls within the purview of section 3D 1.2(d).
. The holding to the contrary in Restrepo has been criticized by other circuits. See, e.g., United States v. Blanco, 888 F.2d 907, 910 (1st Cir.1989), and United States v. White, 888 F.2d 490, 497 (7th Cir.1989).
. The defendant asserts that the inclusion of relevant conduct predating the effective date of the guidelines violates the ex post facto clause of the Constitution, but we reached a contrary conclusion in United States v. Ykema, 887 F.2d *1328697, 700 (6th Cir.1989), cert. denied, — U.S. -, 110 S.Ct. 878, 107 L.Ed.2d 961 (1990).
. Conversely, the defendant bears the burden of proving "facts which would lead to a sentence reduction under the Guidelines[.]" United States v. Rodriguez, 896 F.2d 1031, 1032 (6th Cir.1990).