I think you are correct. You would sell fewer shares if the price was up and pro-rate the NUA and the cost basis entries in TurboTax. A lot of complexity to keep track of but...
I also sold shares w/o regard to the NUA until the balance got down to where the only shares left triggered the NUA.
In my case, I wanted to be done with it and the price of the shares were up so I sold the amount equal to the Gross Distribution.
