We were gathered in the basement mirror room at the Tai Chi centre in Upper Wimpole Street ( sadly long gone )
John Kells explained carefully about two important aspects of single push hands.
Pay attention to the end of your push. Don't just abruptly turn your arm into ward off. Instead, it is as if your arm is being pulled slightly so you enter into the other person to meet their push before it has got going and ward off to catch it.
Pay attention to the end of your Yielding. Don't just abruptly turn your hand over in your eagerness to push. Instead keep the yielding going as if you were going to pull the incoming hand. In this way you are sucking them in to push them.
Suddenly the boundaries become blurred.