So if you you have a “linear” sender (one made for a tank that is a “box” (doesn’t have the spare cutout), it won’t work right because it is measuring only the level of the gas in the tank, not how much is gas is left in the tank.
No amount of bending float arms or repositioning senders will solve this issue.
In a non linear sender, the resistance only changes a little at the top or the tank because there is only a little gas up there. It changes a lot at the bottom of the tank because there is a lot of gas down there.