Try obliterating at least one shield facing first and THEN hit them with the torp. Results are much better.
it can be a bit tricky, cause shields regenerate usually and even 1% of raised shields will migitate teh kinetic damage to around 10% of which only 10% bleedthrough damage gets through to the hull... or something like that...
NPCs cheat, their torps work obviously different for some reason.
Right now, my frontal attack strategy is as follows:
Turn on auto-firing on my two phaser cannons.
Fire a single photon torpedo to help bring down their front shields.
Order attack pattern alpha to boost damage
Order my tactical officer to fire a volley of 4-5 high yield torpedoes.
Divert more power to front shields if necessary.
Release 5 quantum mines.
Engage evasive maneuvers to quickly zoom past and get away before the ship's explosion gets me.
So far, only dreadnought class ships and Borg cubes have been able to survive one round of my frontal assault. :P