I'll be honost, I think that we're getting into the realm of unnessecary detail.

Dionysus9 got it on the nose, simply give the types of weapons different attack ratings at various ranges.

As for specific hit zones on units (if I read that correctly), I don't see how, considering we don't control the units melee combat directly, that would differ from simply taking the offense and defense stat, doing some formula to them, and then adding or subtracting a random number with each hit. It would certainly be more CPU friendly.