ProMods

I have question about this option, on which side i need to put it to be most realistic , currently the slider is max to the left

Left is Off, No torque effect on your force feedback steering wheel.
Realistic depends on the size of the engine/Torque produced, weight of your load, and terrain.
Going uphill will produce a stronger effect IRL since it takes more energy to move the same weight up a hill.
Your vehicle will potentially use more of the torque to get the load started.
The effect will be most pronounced when starting your truck from a stop or when transitioning from flat land (static effort once the load has been accelerated) going up steep grades where there is a distinctive difference in the effort the truck most overcome to maintain speed of the load or accelerate the load up a hill requiring more energy.