Ah yeah I see what you mean, I've had a few shots where it seems to be less than 3 feet away and the guy then proceeds to kill me, only for me to see he has 80% health remaining.

Would it be true (total guess) that the further the target is, the more damage? Ballistic-ally I have no idea but say you shoot a guy 4 feet away and then shoot a guy 40 feet away. The projectile has had more time to get 'up to full speed', with the 40 feet.

I may just be talking out my ass, its just a guess.