Yes, and yes.
There is no question for me that the most consistent way to shoot a side-by-side that I have not had the stock altered on, is to shoot with my left arm, fully extended, and the fore end, laying in the palm of my left hand wherever it ends up.
If you think about the position of it all, it’s the only way to be consistent with rental guns or borrowed guns or shooting a variety of guns that a person may acquire with different stocks and forends.
Because the one thing that is consistent is where your palm is when you extend your arm fully straight out.
And if you watch enough shooting videos, you’ll know that that is a particular style taught in French and British shooting schools for the shooting of partridges with a side-by-side.
I too have my FITASC gun stocked to perfect my mount in competitions. It has to be.
Shooting driven birds with a borrowed shotgun, much less so.