Interesting discussion. I thought of this when finishing my first Model IV. My solution then was to fill the tanks a couple of gallons at a time - both in flight attitude and on the ground.. Yes, the fuel level in the sight gauge will vary according to attitude. The only thing I definitely remember is that "Full" on the sight gauge indicated 9 gallons and above. Empty on the sight gauge and you may still have a couple of gallons, but I doubt any of us would take off with no fuel visible. As a back-up, I added a low fuel indicator that flashed a red light on the panel when the wing takks were empty. A few hours and the sight gauges develop into a pretty good indicator of where you are fuel wise.