The ratio is pretty much pointless. There are enemies with no weakspots (Shanks, Minos etc) and everytime you kill one of them with the gun of your choice it will lower the ratio (how much, depends on your kills you have with that weapon type). My auto rifle ratio is somehwere at +30% with like 29k kills. So it sounds like I can't aim for the head, which is stupid cauz I do headhshots all the time with these types of guns, even in PvP. Scout rifle is somehwere at 43% percent. And I'm pretty much sure all players here in that topic have similar stats.