A320 alt fuel
During FMGC initialization usually we get to INIT NEXT PAGE to inter the block fuel and other info, sometimes I see the Alt fuel is lower than the flight plan Alt fuel (the reason as FCOM 4 states is that the calculation to alternate is based on cost index 0 ),now should I put the alternate fuel stated in the flight plan (which is higher by 200-300kg) or just leave the calculated as is, and appreciate if there is a reference, of course the Minimum Fuel on Board at Destination will be affected.