I have a floppy-eared dog, but thanks to him being so leggy he needed a Giant sized crate even though he's a lab mix. The guidelines imply that it should be top of the ears to the ground, but I think it's up to the airline staff (who will likely err on the side of larger crate as they risk fines if the animal control people decide the crate was too small).
FWIW, my dog is ~30.5 inches from floor to the top of his head.