To raise the point of impact on a shotgun you need to raise the comb, either by bending the stock or by otherwise adjusting it upwards. This is done on competition guns with an adjustable comb that allows a wide range of adjustment and functions similar to the rear site on a rifle or pistol. An alternative way is to use moleskin or rubber pads to move the position that your cheek touches the comb upwards. Again this is analogous to the rear site on a rifle or pistol, moving the rear site (or cheek touch point) upwards raises the point of impact.
Pitch does not change point of impact (or if it does it is very minimal). Pitch is used to change the way the gun responds to the way you mount and hold the gun during recoil. If you have face slap when shooting, it is likely an issue of pitch. Pitch is easily adjusted by unscrewing the recoil pad and placing washers or other spacers on the upper (down pitch) or lower (up pitch) side of the pad. This adjustment changes the relative angle of the butt on your shoulder and when the gun fires, the dynamics of the recoil in combination with this angle move the stock either into or away from your face. This is a critical issue for a gun that will fired many times such as a competition gun.
A very good summary of gun fit can be found on this web site by the US Army Marksman Unit.
http://www.shootingusa.com/PRO_TIPS/USAMU2-2/usamu2-2.htmlLength of pull will not directly change point of impact but on field guns or guns without a “parallel” comb increasing the length of pull will lower the point of impact since the comb height typically drops from the front to the rear. If you increase the length of pull, you move down this slope and will lower the point of impact.
Hope this helps.
Thanks
Z