I would very much like to know where you think the butt stock should engage the shoulder. Should the heel be below, slightly on, or slightly above the clavicle? And what is the proper amount of cheek to stock pressure.
Regarding cheek-to-stock pressure, think about the pressure of a medium handshake: not a death grip but also not a limp handshake.
This is the approximate pressure you should feel on all four points of physical contact with your shotgun: the front hand against the shotgun’s forearm, the back hand in the pistol grip area, the cheek against the comb and the shoulder against the butt pad. There are a number of shooters at the top of our game who shoot with a much softer cheek-to-stock weld and defy this norm but this is the general guidance.
As for the position of the butt pad against the shoulder, we gun fitters look for even coverage between the butt pad and the shoulder, from the heel (top of the butt pad) to the toe (bottom of the butt pad). Good butt-to-shoulder coverage ensures that the shotgun’s recoil is absorbed across the entire area of the butt pad, which minimizes the shooter’s “felt recoil.” A shooter with uneven coverage between butt pad and shoulder will feel more recoil from the toe of the pad against the upper portion of the pectoral muscle.
When there is excessive toe contact and a lack of heel contact, the cause is usually one of two issues assuming that the shooter is in a proper stance: 1) the shotgun needs more pitch (toe angled away from the chest) and often more toe out, or 2) the shotgun needs a Monte Carlo or an adjustable butt pad to lower the top of the butt pad in relation to the top edge of the comb. When mounted, the heel should generally be at or just under the clavicle. If a shooter has a longer neck, sloping shoulders or both, the heel may stick up above the clavicle.
The solution here is either a custom stock with a Monte Carlo or an adjustable butt plate that allows for adjustment of the heel downward, away from the rib-line.