When you or your heirs go to get the money out of a tax deferred account, taxes are owed. So unless the money will be given to a charity, you should make an estimate of the tax burden that will be applied to the residual. Life goes in unexpected directions so you may need to withdraw more than you think or when your heirs withdraw it, they will owe the tax.
Roth math often depends on the nuances of the tax code - maximizing ACA premium credits, avoiding the LTCG tax phase-in, avoiding IRMAA fees, minimizing taxes on SS benefits, beating the clock before TCJA expires, etc. There are pre-built programs where the authors have spent untold hours toiling over the tax code to program that stuff in, I recommend using one of those rather than try to program all that yourself. (Bogleheads.org's Retiree Portfolio Model (free spreadsheet) and Pralana Gold (paid) are both good, I've seen others discuss other tools as well.)
Another major planning factor to consider is the possible need for Long Term Care. Some folks go overboard with Roth Conversions, but it's generally a good idea to leave some money in tax deferred because long term care expenses can be tax deductible. It would be bad to have pre-paid taxes doing Roth Conversions if you actually ended up needing care that could have been paid for using IRA money and a (nearly) offsetting tax deduction.