[Frank0001]

I generally try to hit some 4-5 meters above the ship's depth, but I'm somehow weary of setting torpedoes to 2 or even 1 meter. Something tells me the things are more prone to pre-detonate when they are tossed out of the waves at that depth!

I'm not sure if that's modelled, but I'm still cautious about that
But basically, the lower you set your impact-depth, the longer time water will gush inside the ship I believe. Except with high waves of course.