Cannot help with the modding, but DEEP sets the top to run at 30 feet below the layer or 350 feet if no layer, as I recall.
Note that if you fire at 600 feet and set the torp at LEVEL, it will stay at 600 feet.
In my experience, a MK48 set at DEEP has no problem finding subs below the layer no matter how deep. MK37s are another story, but that is part of the challenge (and fun) of early Cold War subs.
