From a 'feel' perspective, I tend to think of the 'corner' as the muscle contraction along the back edge the body. I think HI spoke of a SCIP (SCap + hIP) ... which is something I can readily relate to ... to me that would be the 'corner'.
Perhaps we need a better term than "corner". "Corner" connotes something angular, and obvious, even pointy. But it's probably too late for a new term.