Sometime between Cramer's Mad Money and Deutsch's vastly inferior but recently much improved, The Big Idea, it occurred to me that when you are applying pressure to the face with the shoulder from the mount, you want to post on the same side that the guy is looking toward.
In other words, if you are using your left shoulder to push the guy's face to your right, then that's the side you want to be wary of him taking you by way of escape. He could turn into you. But if you've got good shoulder pressure, then that's not going to be something you're going to have to worry about not being able to defend.
