One important corollary of pulling the inside foot back is moving the inside hip forward and upward at the same time. If you don't do this thing with the new inside hip, you will be allowing that hip to move back along with the foot, which is identical to rotating the body into the turn, aka upper body rotation. That's bad, oh so bad.
So think of the foot-pull-back move this way:
--pull the new inside foot back
--at the same time, project the new inside hip forward and upward
-------which amounts to straightening out and lengthening the new inside half,
-------which means you are moving the top parts of the new inside half of the body downhill over the new inside ski
-------aka the "strong inside half" move
Doing this two-part movement gets the CoM across the new inside ski, and downhill of it.
It's a hips-in-first thing. The glutes are involved because it's a "hip extension" move.
Edited by LiquidFeet - 11/17/15 at 3:30pm