Really interesting...
http://www.navweaps.com/Weapons/WAMJAP_ASW.htm
Allied the most used allied Depth Charge was the 420lbs. one, with a lethal radius between 4.3 filled TNT in early and middle war times, and 7m filled with Amatol/Minol in later war times.
Japanese only has 220lbs, Depth Charges with a rate of sink of 1.9m/s.
This means the lthal radios must to be much samaller than above for 420lbs.
Sure they needs to explode so near the hull, almos the half of the above values for 420lbs, may be between 2m and 2.5m.
Only after 1943, japanese developed a 357lbs, Depth Charge, with a rate of sink of 3m/s.
The lethal radius for them must be between 3m and 4m only.
Ingame defalut settings are a random value between 4.5m and 40m.... a very unrealistic value...
I changed the lethal radius to a more moderated values, now i am using a random value between 4.5m and 10m, wich is too biger than in real life.
4.5m is about the double of the real life value, and 10m is about 4 times the real life value.
Plus i reduce the sink rate from 5m/s default down to 3m/s wich is near 60% more higher than in real life (1,9m/s)
It is similar i done for SH3, works fine.