I also firmly believe that it takes more force to get an ounce of shot out of a 28 ga. tube than it does to get an ounce of the same shot out of a 12 ga. bore. To end up with the same velocity, I believe more friction needs to be overcome as the bore gets smaller, not just inertia. Fun in a weird kind of way.
When I wrote my arguments here I always tried make them apply to just the shot. You can get into the mass of everything being ejected - shot, wad, burned powder and hot gasses. You can get into the energy expended in deformation of the wad, the deformation of the shot, the heating of the shot, the heating of the barrel, the opening of the crimp, bore friction etc... But the great bulk of the work is expended overcoming the inertia of the shot charge in order to accelerate it from 0 to 1200 fps.
