You're right. I did say that. What I should have said is "the build plate is on top", and not "heat rises", as I was not comparing radiant to conductive heat.
What I meant is probably more clear in my second post: it doesn't have to go up through an aluminum heat sink first to reach the printing surface if the PCB's are facing up and in contact with the printing substrate already.
I wonder if doing this would solve the issue with some people not seeing adequate bed temperatures.
There is a scrap of some 1/2 inch wool felt here that I might pad the bottom of the heat bed with- that is also on the same page I linked regarding ways to retain heat on the print bed. I might have to longer screws and springs for that, though.