Actually, for us, the goal is to have the market, IRAs and any Roth accounts all depleted at the same time as the heart, liver and other organs. ;-)
The exercise/question/spreadsheet is more general, trying to see if there is a financial benefit to convert IRAs to a Roth for those of us old enough to draw on both accounts. Since Roths are attractive for their tax free growth, the question is whether there is a financial reason to go thru the brain damage to convert IRAs to a Roth.
It would seem that taxable resources should be depleted first taking only RMDs from the IRA, allowing as much as possible to grow tax free.