Kwun sau: In the WC I train, we also seldom raise our bong sau so high in dan chi. Although, as
Mook pointed out, it does depend on the direction and force of the incoming punch, and that is not possible to determine watching a video. It must be felt. Regardless, in my WC we do not attempt to lift up our bong sau. If our opponent's punch has a "heavy-elbow" and comes in straight, his force rolls and bends our arm into a mid-level bong sau.. If he presses down forcefully and strikes low, we let our bong bend down with his force. If he punches high, often we can slip his force and straighten our arm into an inside gate punch to deflect his punch. That is the typical pattern. A low punch rolls us into a low bong. A mid-level punch into a mid-level bong. And a high, extended punch is countered with a deflecting punch. And, if he steps forward and drives through heavily, we let his force turn us and deflect his punch
laterally, not vertically.
You must understand, that we do not make our own defense. We do not intentionally bend our own arm into a bong. Our opponent's force bends our arm into bong sau. His energy determines the shape of our bong. About the only kind of punch that would shape our bong into such a high bong sau is a close, elbow-heavy rising punch. That happens, but it's not the norm in dan chi.
This is the key difference I see between the way many other WC branches practice dan chi and the lineage I belong to. In dan chi most groups seem to counter the initial palm strike with a shape downward jut sau, followed by a punch which is, in turn. countered by a lifting bong sau.
This leads to a pronounced sinking and lifting cycle in dan chi that is very apparent when views from the side. By contrast, we counter the palm with a very minimal jum sau, and then respond to the following punch, rolling into bong but not forcefully lifting our arm. So seen from the side, there is far less vertical movement.
Check out the following clip made by a guy from more or less the same lineage as me to see what I mean when I say that our opponent makes our bong sau: