The general take from OP, definitely can't count on Des Moines with anything less than a 3, and a 2 would be ideal.
And correct it too soon to think about it too much, but speculation/projection is fun.
For thought experiment, looking at who's near the top 4/5 lines currently, some of the SEC could gravitate toward Orlando or even Greensboro for some of the slots, freeing TCU/Texas/Houston for Birmingham. Duke and/or UNC almost always gets at least one in Greensboro, but both are below typical levels and who knows, maybe wouldn't even be at 5 seed level (but a LOT of season left and lots of wins available in ACC). As it is now, Virginia gets one of those.
A ton of moving parts. Bottom line I hope ISU just continues to win a lot and if we get high seed with advantageous placement, that's bonus material.
Lets say Auburn is 5 and Texas is 8 and Iowa State is 12. Auburn would get Birmingham, Texas would get Des Moines and Iowa State would get Orlando.