Specializing in the resto / repair for classic cars for ~25 years I have lost hundreds if not thousands of hours fighting the issue across all makes and models. The compensator made by Tanks sometimes will resolve the issue IF your close (within 1/4 tank). Several years back Spectre said they were going to resolve the issue but gave up. Myself I don't understand why it is so difficult. They will OHM out correctly on the bench, and in and empty tank flipping it upside down for full. In the car with fuel, usually have to settle for being off at full or empty. I have chosen to read 3/4 when full and empty when a gallon or two is still in the tank.
I'm beginning to think it may have something to do with the buoyancy of the float, possibly coupled with today's fuels or weight of the arm