Different rep for same Vets?

[Lib Feathers]

I tried searching the forum but couldn't find the answer, so I'll ask the question here. I've noticed when I'm "bowling" on Kingshead, even though all 6 Veterans are lvl 18, I get different rep points for killing them. Same Vets, same grenades, yet I may get anywhere from 5 to 13 points for each one. Why is that? Is it related to the number of hits it takes to kill them? I can't tell which ones I've hit how many times when they all clump up together, so I can't say how many times I hit each one.