If you gained faction when you lost, i'm betting your answer is that you gain faction when you lose.
Most of the random 8v8 and challenge missions give you faction based on how well you did while in there. Alliance battles give you faction for losing also.
Errrr... I think Former Ruling is correct, the better you do score wise/time wise the better faction you get. Im thinking 750 is max cause i got that amount like 3 times in a row when we had a winning streak at Fort Aspenwood.