I was having experiences similar to those being expressed by some in this thread, i.e., you fire a couple torps and BAM, enemy snaps off a couple reaction shots . . .
Then I started paying more attention to:
(a) getting into silent mode IMMEDIATELY
(b) possibly slowing to a crawl of 1 or 0 knots
(c) possibly changing depth if that seems beneficial to remaining undetected
(d) focusing on the "Signatures" tab and trying to actually get the hang of identifying boats by their signatures
(e) once those identifications are getting pretty good and/or actual courses and speeds are coming in, then it seems one is "in business" as far as "being a silent hunter"
(f) once you have a contact well identified, you can see what his estimated detection levels of you are, and by using those to judge when it is safe to fire a dog-legged shot and then turning them at the bad guys once they are reasonably clear of my position AND then also turning my boat so that I am running on a course roughly parallel to the torps
Using these better practices, I've noticed I've got a LOT less quick response shots down the reciprocal bearing of my torps, and in fact have managed a half dozen or so kills where I scarcely needed to evade a torpedo at all; they fired at a bearing that was a couple thousand or more yards off my axis.