You could try the mod in the below link.
https://www.mediafire.com/file/3mat4...power.rar/file
To be intalled with JSGME. In this mod I changed the min and max damage values of the torpedoes in the
torpedoes_g7a-e.zon file. With these values one torpedo is no longer always enough. Especially larger vessel often require 2 torpedoes. It is far from perfect but I think it is an improvement. At least now there is some uncertainty and you will be forced to use more torpedoes on juicy targets. This should reduce the tonnage scores somewhat. This mod was just an experiment and I could not really get the results I was looking for and testing these results was very time consuming. So there may be better values than I use but I think the ones I use work reasonably well. You could try it and see if you like it. Test the results yourself using the "new merchant fleet" test mission.
Note that with the values in this mod quite often when you hit a vessel it has no effect initially but after a while, sometimes a few hours, the vessel will suddenly drop out of the convoy and either sink or trail behind at reduced speed. It will also leave vessels dead in the water occasionally requiring a coup de grace.
As I have no Mediafire account this file will only be up for two weeks.