I feel that by providing space above the broodnest we are creating an unnatural situation that the bees quickly remedy by filling it with comb. A wild colony would always start building at the top of the cavity and build downwards, there's never an empty space above their heads if left to their own devices. Thinking about it that way, the Warre has to be the most natural one, with 'supers' always added underneath the broodnest for expanding downwards. (I know they call them 'nadirs' instead of 'supers'.) (Still don't know how the Stewarton is managed.)

Warning:
Read the next bit only if you have had your tea already!

There's a rather macabre story which seems to be fitting into this thread:
During our Ghana-trip in January I heard about a taboo source of honey. It's honey from graves: Feral colonies can occupy the chest-cavity of corpses in shallow graves, possibly using the ribs as natural top bars.

... you have been warned,
Doris