well ps2 has some odd ways of calculating rank/skill... not totally sure exactly how it does it
but 1 thing.. i use custom weapon weights.. which means killing ppl with (or being killed by) certain weapons will effect your skill differently depending on the weapon... im not gonna post exactly what they are.. nor do i really remember anyway.. but for example.. using MG/Sniper and whatnot will affect your skill a lot less then using weapons such as pistols or other 'not-so-devestating' weapons..
i also have skill decay on.. but its at a pretty low value.. basically i think thats set so each day you do not play.. your skill goes down by a few percent or so.. but if you dont play for a couple days it isnt usually noticable.. but if you dont play for a week.. dont expect to be ranked #1 anymore
(this also helps rid the stats of ppl that play 2 or 3 times and are in first or so then you never see them again..)
ps3 is supposed to be much better when it comes to calculating skill and such, but its not totally dod-friendly and a bit buggy (not to mention my theme wouldnt work on it lol).. a couple more patches and i might try that out again..