So after many tests in my current career, i have added few mods and adjusted some (like IRAI difficulty HYDROPHONE_DIFFICULTY_MIN = 0.40; HYDROPHONE_DIFFICULTY_MAX = 0.60; SONAR_DIFFICULTY_MIN = 0.40; SONAR_DIFFICULTY_MAX = 0.60; )
Added a nice mod (thanks Volodya!) ---> AST_SH5_v2 by Bilge Rat.
At least now, small cargos are sinking, and not sitting there (or keeping speed) burning for hours! They can sink from 5 mn to >30 mn depending hitting place.
Bigger boats still need more torpedos, but medium can be sinked with one if we can wait.
I have also reactivated "AI crew damage control" in TDW patcher, to give merchants more chance to repair/stop the sinking.
Very pleased the way my mod list is running