Income is taxed according to the tax brackets. The first taxable portion of your income is taxed at 10%, then 12%, then 22%. If your overall average is 16%, that probably means that your top marginal tax rate is 22%, and any additional income will be taxed 22%. Don’t forget state income tax.
Also, remember that any required minimum distribution, that you said starts next year, is not eligible for conversion. After you have satisfied the RMD requirement, any additional funds you withdraw are eligible for conversion.
