Analogue Plunger for Pinball FX2

Hi,

I am using an analogue plunger with an analogue potentiometer in my pinball cab. It is working as Z axis.

My problem is when I pull the plunger Pinball FX reacts only when I pull it out about 2 inches and stops after 3inches.Only a very short way from the whole thing is used.
It is mapped to right thumb as x axis

Is there a way to calibrate this or something that I can do to solve this?