This might illustrate it in a more comprehensive manner (se picture).
So, one of 3 things (or a combination of the 3) is possible in my mind:
1. Wrong sensor plate zero position or incorrect clearance between sensor lever and the control plunger (the basic position = the 1-2 mm of free travel from zero position until resistance [with ignition/pump ON]) .
2. Wrong potentiometer zero position/misalignment.
3. Bad potentiometer.

Attached Thumbnails