The performance info in the FCOM is all based on 33% MAC. Why would the aircraft be at 25%? The takeoff MAC should be close to 34% so that during the flight as the fuel is burned off the MAC will move from 34% to 30% or there about. Since the performance figures are based on 33%, then the 'plane should be loaded accordingly. I would suggest reaching 33% at the midway point of the flight.