...was it one of Kenneth Chung's people? From what I can tell he made some...err...changes since the 1970's.
I think it's fair to say that Ng Wah Sum's and Eddie Chong's early (hell, even present) stuff is more representative of what Leung Sheung actually taught than whatever Ken teaches now.
Regardless of the specifics of Chi-Sau, I think it's success starts with the attitude of the Novice. I see a lot of people new to Chi-Sau take what I think is the wrong attitude. The guy across from them gives em a wack. You can literally see the facial expression change, now it's about wacking back. They do and it becomes a loop. Now that is where you should be eventually but as a new person to the Chi-Sau imo your first thought shouldn't be "I need to wack em back", it can't be about ego, your first thought should be "hmmm what did I do wrong there?" If that means not taking an opening so you can more closely watch what you are doing wrong (in the event you repeat the mistake) it will help you in the long run.