Spread is only there to simulate the difficulty of firing a gun. It’s only real-life equivalent is recoil. Though just putting recoil in a game is not enough.
My point is, if you’re looking at guns then it would make sense to think that big guns have more recoil than small guns, but this doesn’t mean that they’ll have to have more spread all the time. A big gun is actually easier to fire from a stable position than a hand pistol is (and therefore deserves less spread), however, a light pistol is far easier to use while moving than a bigger gun and so moving should have less effect on the spread of a light weapon than that of a big one.
And the same thing for body types. Someone with a good condition and who’s used to running fast all the time will have an easier time aiming a gun on the move than a big bloke in poor shape (so light bodies will have less spread on the move). However, big arms will have an advantage in holding a gun steady so heavy guys should get less spread on while standing still.
I’d like to see different spread behaviours for the guns as well as the bodies. If you only apply it on the guns than there will be less incentive for heavy guys to use light weapons because they will always be out moved by light guys holding the same gun. They’ll need a spread tailored to their slow body type, and get an advantage in shooting from stationary positions.