SQQ: the answer to your question is this:
In the swing dances, the vertical component of the center of mass movement does not cycle on a step-by-step basis, but instead occurs across cycles of typically three or more steps. Just looking at one step in isolation is not enough - you have to look at the group. Chances are you will find that the highest alittude is over a standing foot, and the lowest between feet between 3 and 1, though for some of the italians it might be just before they arrive over step 1.
And for tango of course the center of mass altitude is supposed to be constant.
Discovered something interesting btw... if running down the street carrying something you don't want to bounce, run with tango action...