The $400 was an original refund. My deadline for the 3 year to amend timeframe will run out after tomorrow.
I ran the 2020 amendment through the Turbo Tax "2020 amend" program following your suggestion and indeed there was no increase in my refund. AN odd relief that apparently I'm not leaving anything on the table.
It appears that, even though my AGI amendment lowered my AGI considerably, it does nothing to further increase my refund (my original refund was about $400) like I thought it might. Apparently, reducing liability (in my case) does not always translate to a larger refund.
