How to report 1099-R Tax Withheld from Rollover IRA conversion to Roth on lines B4, 5 and 6

I converted $45,000 from my "Rollover IRA" to my "Roth IRA".  I also had my investment company withhold 10% tax.  The 1099-R has lines 1 and 2a as $45,000, 2b taxable amount not determined selected (x), line 4 Federal income tax withheld as $4,500 and line 7 Distribution code as "7" and IRA/SEP/SIMPLE (x).

After entering the 1099-R, Turbo Tax populates line B4 of Form 1099-R with $45,000 but leaves lines B5 and B6 blank.

My understanding is the full $45,000 is treated as a distribution, but after withholding $4,500 for taxes, shouldn't TurboTax be recording the ROTH contribution as $40,500 on line B6?  (or, am I over complicating the meaning of Line B6 since the difference was all Federal Taxes)

Thank you