"Perhaps the conclusion to be drawn is (in contrast to the initial text-book type answer that there is a clear difference between W and FT), that there is no difference in absolute footrise as long as whatever foot rise is used is in character - which mainly means that is the relative foot rise and the dynamics from step to step that is more important. Certainly the dancing of our top competitors seems to bear that out at least on a first glance."

There are pretty obvious differences in the rise and fall between most dancer's feather vs. their waltz natural. Two basic ideas may help you understand this:

1) Waltz rise is more of a deep, underhanded swing. Instead of dancing over the foot and leg on the second step, you dance through it, continuing to rise in the foot and knee during the second step. In foxtrot there is very little continuation of foot rise during the second step (officially none), but there is some incidental gain and then loss of altitude that occurs are a result of the legs closing and then reopening.

2) Waltz figures which close the feet and then lower from this position rise enough that they can fully absorb the previous energy of horizontal movement into potential energy of body altitude. In effect, the rise until they "stall out", the movement all but stops, and we fall on a downswing path that is initially almost purely vertical, gradually curving back into horizontal. In contrast, foxtrot passing movements absorb only a fraction of the movement energy into rise, so that the body slows a little but does not stop. The peak of the rise and transition to fall is much more gradual as the vertical component at the end of step 2/start of step 3 comes only from the closing and redividing of the legs.