The bottom barrel is more in line with the lengthwise axis of the stock. Thus directing the recoil directly into the shoulder with minimal muzzle flip.
As for the high rib. Having the high rib theoretically places the rib in the same location, vertically, as the rib would be on a O/U gun.
As an aside, you may notice the rib on a trap gun is adjustable to change the POA/POI. As a rule trap guns shoot high because of the ever rising targets.
Oh, and by the way, it is a shotgun, not a "shotty" but I will ignore that..........