The tag MapHardness is only called 2 times in sources. When it is read from the SMD, and when baseStrength is calculated (baseStrength is used to calculate the size of the crater).
baseStrength=-pow(strength,0.6f)*3/mapHardness;
So in fact, it take strength, which must be the power of the weapond, calculate strength^0.6, multiply by 3 and divide by mapHardness.
So it shouldn't crash the water like it does.
(if any one understand why it is -pow(...) and not pow(...), tell me :). And another fun stuff i will test, MapHardness is float, so it can be negative :))