It makes sense to me. I retired earlier this year and I'm in a similar situation where I can do partial Roth conversions to the top of the 12% bracket over the next 6 years (before I turn 70 1/2), but when all is said and done will have only have converted about 25% of my current traditional IRA balance.
Before I gave this much thought, conversions seemed to be a "no brainer" because in my mind I was saving 10% in taxes by converting early at 12% versus RMD time in the 22% bracket. But after thinking it thru, I see that it takes time to "realize" that full savings, although I hadn't spent the time to quantify just how long it would take.
So, I have some decisions to make before the end of the year. I can go ahead and start doing Roth conversions. Or I can take advantage of taking some capital gains in my taxable account at 0% tax while I'm in the 12% bracket. Or I can take some distributions from my IRA now for living expenses (instead of from my taxable account), thus reducing future RMD's. Or I can do some combination of the above.
Retirement can be complicated.
This is a fairly common misconception. Roth conversions are break-even from day one. There is no payback period nor TVM impact related to the prepaid tax. (...unless you do something silly, like convert into a bracket that's significantly higher than what you'd otherwise pay with RMDs).
Reason:
Embedded in your tIRA is a tax liability that grows in lock-step with the taxable funds that could be used to pay tax in a conversion. IOW, when you continue to defer, the embedded tax liability continues to grow by the same amount as your would-be tax dollars on a conversion. When you convert, it's really just like paying off a liability early in the hope that the liability will be less today than in the future (due to tax rate differences).
Example:
Assume: tIRA of $10K, taxable account of $1.2K, tax rate 12% now and 12% later, rate of return 7%, and 15-year timeframe.
If converted, obviously the tIRA and taxable go to zero, and the Roth of $10K grows to $27.6K at 7% over 15 years.
If not converted, the tIRA grows to $27.6K and the taxable account grows to $3.3K, which is exactly how much is needed to pay tax on the $27.6K tIRA. Net after-tax proceeds are exactly the same as the convert scenario.
Again, there is no TVM impact nor payback period associated with prepaying the tax liability. This analysis could be done at year1, year5, or year10, and the answer would be the same.
Obviously, if you assume the tax rate is 12% now and 22% later, the convert scenario wins easily. In actuality, the convert scenario wins even when the tax rates are the same. In the convert scenario above, the $1.2K taxable balance was, in effect, "transferred" tax-free into the Roth. No tax will ever be due on the $1.2K going forward. In the no-convert scenario, the taxable account grows to $3.3K and will inevitably have some tax due over that period of time. So the real after-tax value of the no-convert scenario is less than $27.6K, but this is negligible compared to the effect of tax rate differences.