That situation is easily fixed by using an L-shaped float wire.

The float on an L-shaped wire still has the same curved path
that it would with a straight wire. The better fix is an extended
sender that puts the hinge in the centre of the tank.
An even better fix would be two or three senders, wired
in series, at different places in the tank so that they would average
out the dihedral effects and so on. The capacitance-type senders are
often used this way in larger airplanes.
The best fix would be several capacitance senders feeding a
microprocessor that has been programmed for the tank's shape and
dihedral effect. The chip would drive the gauge. Probably been done,
somewhere.

Dan