I don't think it's so much the matter of actual TP feed, but I believe the larger a chunk of damage done, the higher the possibility a mob will react with a TP if it has TP. I find things like Shadow mobs are more sensitive to this behavior as darn near time I can think I've WSed them and them still being over 25%, they almost always counter with Dimensional Death if they have TP (And given the +3 thing, it usually means they do).