As said, thats a weapon balancing issue - the fact that Damage/time values for weapons are all over the place (with say, semi-auto pistols being much worse than laserbeam cannons), rather than anything to do with skill influence factors (which, seeing as it's pretty easy to get ~130% damage on most weapons, and next to impossible to get past ~155%, wouldn't explain the gap you describe anyway.

(Oh and yes, the damage% is a simple multiplier on the weapon damage)