Problem with field guns is that they have a lot of drop a comb, stocks are not parrel to the barrels so the angle may differ from gun to gun. If all your stocks were the same they would have the same angle. I'd rather check poi and fit of stock against shoulder when mounted and shot. The wall trick just gets me into a close range I'd what works for me.
Trap and live bird guns are often setup to pattern high and changing the pitch can help. I have a Fox 20 ga. with 26" i/c and lt. mod that I shoot well on quail and low gun Skeet which is setup like a trap gun. Most of my shots are on rising or just leveling out birds so high poi is no handicap. Our quail shots tend to be very close and fast with long range shots almost a rare thing. If birds were all level or dropping I'd shoot over more than a few of them. But if I shoot it high gun at Skeet my scores go down. Since it works for its intended use, even though it is not setup like I would normally set such a gun up I just shoot it.
Sometimes you run into a gun set up for either a freak of nature or a nut of a shooter. One late hunting partner was 6' 10" with arms and neck twice mine but a fairly small chest. He shot 16 3/4" lop on his duck gun. Just added a slice of 2x4 under the recoil plate. Colored it walnut and shot the gun that ways for years. Or the Skeet shooter who mounted his gun almost in the middle of his chest. He had taken a rasp to the stock and removed almost all of the comb where his face touched. He adjusted the pitch until his poi was where he wanted it. Used both eyes and was a heck of a shot. Point is tha gun fit is a personal thing and what is normal for you is all that matters.
