Shooter's style could effect what angle keeps the butt in full contact with the shoulder pocket. Bunker shooters of any experience all seem to lean well forward, probably so a 'grass cutter' does not come out under the barrel. I would think they could do with less pitch than a field shooter who is not so likely to lean into the gun. Some shooters may not be strong enough to lean, and want almost to bend back to get some leverage to hold up the gun. They would get whacked w/o down pitch - it kills them because they lean back, and they lean back because it kills them.
High angle shots - straight up, etc. might be easier with near zero, or up pitch. Depends on flexibility and style. People who can bend the upper body well back could use the same pitch as for lower targets. People who do not bend back much would get better shoulder contact from higher pitch when the gun is pointed high. Depending on the layout, a gun dedicated for driven shooting might work out better with less pitch.
