Instead of loading 25/50/75/100% in each tank, how about something like(based on 600l in fuselage, 400l in wings):
100% = 100% in all tanks
75% = 100% in fuselage tanks, 37% in wing tanks
50% = 83% in fuselage tanks, 0% in wing tanks
25% = 42% in fuselage tanks
Similarly, for the Fw 190A-8/F-8(based on 525l in fore+aft, 115l in aux):
100% = 100% in all tanks
75% = 91% in fore/aft, 0% in aux
50% = 61% in fore/aft, 0% in aux
25% = 30% in fore/aft, 0% in aux
And the same goes for the Macchis with their tiny wing and aux tanks, and any others I haven't thought of...