Dear Don,
I really doubt the necessary of that rear foot flat pror the body weight transfer from fron foot. I believe the body weight distribution between steps is similar in all dances , except with the particular figure. I prefered lower rear heel for straight legs and body weight is split or nearly split at this moment. Could I use the rules of 1. contra letaral balance 2. foot ultimately underneath the same side shoulder , hip maximum open ( rumba backward walk )? My female latin coach emphasized flat rear foot with no body weight trnasferring at that moment ? For me , it is painful.Of course , if I am wrong , I am appreciated to give up my opinion.
YLChen

Yichen. I would listen to you lady teacher. There is no wieght until after the foot os flat on the floor. The feeling is like squashing a soft fruit. As the weight is transfered the front knee should turn inwards slightly, still with a nice leg line, and a high instep.This is when you pass the hip over. I would watch for this with your teacher. Don't forget to have both feet turned out. see if she very nearly gets a toe to heel on that backward step. No gap between thighs. With all that you still have to smile. Good Luck.