Perhaps the old proximity gold/xp system? Or something like: If a player kills another they could get the slain player's level/2=gold and level*2=xp with the old proximity mechanic. For some players this will work out to a normal x4--5 but for others it'll be a regular-ish match.
So long as the server remains small there shouldn't be much of an issue with crowd control due to the proximity mechanic.