Right, if I change FWH to boil hopping, it will be different. And if I leave FWH in the wort for 48 hrs, that will probably also be different.... but what about the theory of putting the FWH in when I'm heating the wort up to boil, and "steeping" them there for 20 minutes or so at around 140F, which is almost exactly what happens when you FWH right out of the mash cooler (my wort is usually 130-140F, and I have it boiling within 30 minutes....) It's just that the wort has been chilled for some time between, and then reheated thru mash temps to boiling. Is there some enzymatic activity coming out of the mash that has been halted or slowed by the chilling of the wort that will effect the FWH?
i think that's gonna be your best alternative. Seems like it ought to work.