Your "rear sight" on a shotgun is your eye. Moving that up and down is the same as moving it on a rifle.
You have to mount and have the same cheek weld every time on a shotgun so you can be consistent.
Raising your head in essence raises that rear sight and your poi will go up. Left goes left, right/right etc.
Not owning a benelli at this time or having access to the shims I can't tell you which is which but - you want the shim that raises your eyes.
