Thank you, andykyle, for posting here. Your post reminded me of this posted conversation, and I read it again. I also watched the aperture corner development video again. When I repeated the exercises just now with two fingers and then with a single finger between the teeth, I notice some pressure on the fingers from the center of each lip, i.e. top and bottom. I am unclear if this pressure is expected from “positive” lip tension due to corner tightening or from pinching in the middle. The pressure sensation is subtle, but it is there.

How can one determine if the center top/bottom pressure I describe is expected or if it is related to pinching?