[Fishmachine]

From what I can say, the critical spots of T2/T3 are so small, that if you don't hit it accurately enugh, than you just cause minor explosion of fuel, but not sinking. The reason, why you cannot hit them accurately enough is switching from fast TI to slower TII/III's. They tend to slow down with range (especially TII's) and are less accurate than TI's.
For electric torpedoes, just aim them a meter below keel, at 1/4 of the ship length to front. It kills any T2/T3 in 90%.