As an experienced shooter, when you mount a shotgun you probably have an idea of what feels good and what feels a little awkward. That's a good thing. BUT, you're probably looking down the barrel and "aiming" it at something. That's NOT a good thing unless you're maybe hunting something using slugs.
Hopefully the person that did your intro session made it clear that shotguns shooting at clay targets get pointed, not aimed. That being the case if a shotgun feels pretty good to you as an experienced shooter, it's probably close enough, fit wise, to get you on your way WITHOUT experimenting with things.
With your small bore 'experimenting', a 1/2" MOA improvement showed up immediately and you knew that xyz worked better than what you did before. With shotguns, you're shooting roughly a 30" "bullet" at a roughly 4" target, that's moving, so it takes major technique improvements before little things like an adjustable rib does anything you might notice.
LOP changes or adjusting the comb can help a bit with technique but before shelling out big bucks for a gun with all the whistles and bells, get one that feels good and is close, like the Browning you shot, and spend the extra $$ on targets and maybe some lessons from a qualified instructor.
Oh, and welcome to the addiction!!
