Some cabs are not central
Some lean due to worn mounts
In a ideal world set up a AB line in a field,
Drive a peg in the ground 1meter from your wheel marks
Drive past on autosteer and measure the outside edge of your combine cut /wheel rim on tractor etc to the peg
Turn around and drive back on autosteer, measure at same point on other side of machine.
Either move the antenna to centralise the result or set offsets in agopen to centralise
Repeat untill same both ways