I remember doing Chi Sau with Fong Sifu, and being part of the "helper" group as well! That was too many years ago! One of Fong Sifu's teaching methods is to roll with a student....he puts the student in a bad situation, then he asks the "helper" group that is watching to make suggestions for what the student's response should be. Then the student does what was suggested the group and Fong Sifu simply flows with it and puts him/her in another bad situation! It lets the "helper" group start to analyze what is happening in Chi Sau and see what various responses might be as well as their consequences. I remember Fong Sifu as being very smooth and technically precise in his Chi Sau.
I remember training with Joy as well! Good times! One thing he would make us do is take off our shoes and walk cross the floor only by grabbing and dragging with the toes to strengthen the muscles of the feet! One time I was helping Joy do a demo at a fitness center. I had the pole and he had the knives. I did a motion where I swung too wide and hard with the pole (I didn't know anything about using the pole at the time) and Joy blocked with the knives and the end of the pole snapped and flew across the room! He just went on like he expected that to happen!