You miss something.
DT in the ammo counter shows 1 gallon more fuel than is in the droptank, that is when its empty it still has 1 gallon and can be dropped.
So the ammo counter shows 53 gallons per tank but it would be 52 gallons per tank.
E6B shows 104 gallons per droptank.
So the E6B shows exactly double the ammount of droptank fuel than what it has.
Or, the droptanks show half of the fuel what they have.
EDIT
Tested fuel consumption.. when you run on external fuel the aircraft uses up double as much fuel as when it runs on internal.
That means the amount "fuel remaining" shows the fuel for the droptanks of the ki double BUT when you burn droptank fuel it uses twice as much as if internal.
That means the overall flight time is correct, just the value of remaining fuel is doubled.
ps i checked in ta and i checked external and internal tanks, so my reading is not from the 2times fuel multiplier.
EDIT2
Same bug on ki 61, 110G2, 109G6
Probably all planes that have liter droptanks?
In fuel remaining double the value of the fuel in the droptanks is added... dt ammo counter reads correct gallons.
To be honest, fuel remaining does not say it is in gallons but i asumed it since it shows the internal fuel in gallons, according to the use of gallons per hour... if you run 10 mins one tenth of the listed gallons per hour are deducted from remaining fuel.
It also shows external fuel in gallons for p47.. probably all gallon droptanks? but not for liter droptanks...
EDIT3
I always thought ki61 with droptanks feels VERRY heavy. Maybe, the droptanks are figured in with to much wight when full?
ciao schutt