I refuse to believe, that as a gun dealer & whatever else you have to do with guns, that you do not better understand gun fit.
So for the purpose of your temptation to argument I will again state that the shooters eye is the rear sight on a shotgun.

Nearly every other sight system on firearms is adjustable. Rear sight for both wind age & elevation & front for wind age & elevation.

Even though the sight system on a shot gun is not supposed to be squinted along & aligned like a rifle, the sight picture is still important.
The stock fit is what adjusts the gun into the persons sight picture correctly so that the gun shoots where the eye looks.
Wind age by cast & comb thickness & elevation by drop at heel & comb height.
Why is this so difficult to comprehend ?

If my golf club is to short for me it will cramp my swing & effect follow through.
If my A class catamaran sail is not tuned to my weight then the sail will belly & depower.
Like wise to lure fish for flathead while wading on sandbanks & use a uglystick boat rod may catch a fish or three, the cast & retrieve are going to be a bit laborious.

Do you ever find that after your wife or kids have driven your car that the seat & mirrors need to be adjusted back to suit you ? Or do you just drive off all cramped up under the steering wheel & hunch over so you can see in the rear view mirror ?
I think that adjustable seat slides in auto's are over rated.
If you can drive, then you can drive, what has the seat to do with anything. It is just a place to put your butt.
The mirror is useless too. You should be looking at where you are going & not where you have been.
O.M