Another thing I like to play with on the inside vs outside pitches is watching the sequence of toe touch, hip movement, and heel.
toe..hip...heel
toe...hip..heel
hitters have to be able to adjust on the fly, be it the timing of the uncoiling, the hand path, the hand rotation, etc. If they are uncoiling upper and lower body at the same time, those adjustments become difficult because they have committed the hands and barrel too early.