Laz,
I would think that 25% fuel would allow moderate and long range aircraft to reach a fight inbetween to close fields.
I always calculate a 25% fuel tank for a Spitfire to reach another field and this is almost always generous.
P-51s, F4Us, Zeros, Ki61s, P-47s, F6Fs and N1K2s should all beable to fly to a field and then fight on 25% fuel.