What missions did you play specifically (all missions)? Does it rely most on kills, and do deaths factor in at all?
What I mean is, can you just play Blood Gracht on body count with a bunch of other people using rocket launchers, dying almost as often as you kill, and still get high in the rankings based on body count? Because I find that kind of fun anyway. I'm not exactly the best at scoring points in missions, though I do contribute in other ways.
I've tried to figure out how it works, but nobody has satisfactorily answered. Since a bunch of people have it now, maybe someone can tell me.