I believe.....
That turns start at the core, although the upper body does have much to do with initiating, maintaining, and finishing a turn. But, when done correctly the rotation is not very noticable or detectable.
Starting from the ankle up is like saying the car turns without first turning the steering wheel. At the same time, you don't want any "play" in your steering wheel either. Meaning, when the upper body moves, the core moves with it, allowing the legs to be put in a powerful, balanced, and athletic position.
The upper body needs to be put in the right position so that when the effective edge is engaged the lower body can be positioned correctly to hold the edge.