Capacitive sensors vary widely with the amount of ethanol in the gasoline, unless there's an always-immersed "reference" at the bottom of the tank.
Gasoline itself has a fairly consistent capacitive coefficient. Ethanol, however, is 10x greater than gasoline. Gasoline blended with 10% ethanol reads twice as high than 0% blend- so a half tank will read full. Unless you've got that immersed reference at the bottom which reads the same regardless of level, sensing only the fuel's capacitive coefficient. Also, note that capacitance varies somewhat significantly with the fuel temp. Either temp compensation- or that immersed reference- will compensate for it.
Nowadays, most gasoline is blended with ethanol UP TO 10%, but there's no telling what the actual content will be. Might be 5%, might be 10%. Depends on the season, for one.