Hello, Im the author of Natural Sinking Mechanics.
Ive figured that many skippers (especialy those who came from sh3) always try to set up their torpedoes as deep as possible. While the reasons are obvious, youre trying to maximaze the damage by hiting the keel.
However ive found something interestning when i was working on the last version of the mod and looking into compartment layout of every ship, and learning about how the damage system works.
Now at first take a look at these picture, i took it while i was modeling the zones.
it shows the compartment layout of kinposan maru. Red colored parts are the keel, engine rooms and fuel bunkers. Clear are the main comparments. Blue are ballasts and green superstructures.
Now what happens when a torpedo strikes a ship (somewhere). Basicly it generates a bubble, lets call it damagerange. Every compartment that is inside that bubble will take damage. The special about the keel is that it has a small chance to break the ship in halfs. Now the damage range is set so high that the torpedo will always damage every compartment in a fair distance around the impact. Meaning you are always damaging the keel and the main compartments above every time you hit a ship, the depth doesnt matter. I agree that its not quite accurate but thats how the game is designed. So basicly you can forget about torpedo depths.