Would there be any way to let you specify full and tabs levels for fuel in the air-craft config? It would reduce the risk of finger keying mistakes on weight and balance and shouldn't complicate the interface if not set.

I had this issue as well initially, I have solved it by putting the tab quantity as the default fuel in my aircraft profiles. Defaulting fuel to any other value makes no sense to me (0 is silly as I don't fly sailplanes, all other values are totally arbitrary).