I always assumed it was just where the sensor is placed in the tank, maybe on on side so when turning or braking the guage shifts depending on the lean of the gas during say right turns or forward when braking

 

about a 1/8th of a tank in my car is cutting it close.
if you take a turn sharp your gonna sputter and lose power.
haha
also the whole stopping and the needle goes down and and accelerating and it going up makes me nervous sometimes.