One of the unique aspects of Master Chen workshop is his hands on instructions. He will let students push hand with him in any fashion, he will give you a counter and teach you how to do it. This is my third workshops and I have started to get a feel on how to do push hands properly.
Master Chen told us that most people want to push during push hands, but that is not Tai Ji. We should useto do take down, and only use pushing motion to set up a good position for the take down. The upper body should be not power up, it is just a modulator to aim/rotate and a conduit of power from the legs.
In the posture there should be an additional force vector to the ground, this gives the position more stability and power. Most people only have one force vector toward the opponent, this is inadequate.
Master Chen also introduced me a Tai Ji concept song chen 松沉, which means relax and sink. I am still mulling over the meaning of this. I think this is related to take down technique, where you let O force into an empty space and using the force to let O fall. If other students have insight on this term, please write comments.