@dmertz please.
I don't know why the amount is even required, as long as you satisfy it. (If you are over age 70-1/2, you can't rollover your RMD into another plan, like a Roth IRA, so that would be one situation where Turbotax would need to know what part of the 1099-R constituted the "minimum part"; but this is an inherited pension, you say, and I don't think you can roll that over anyway?
If you withdrew $500 but received $300 after tax withholding, then the amount of your withdrawal is still $500.
