Well the theory behind this is that the longer column upon ignition deforms more shot from the jolt it is given. Also with the same amount of shot the number of pellets exposed to bore rubbing are greater in the smaller gauge. That said at least as early as 1910 when a normal shell was loaded with a card & felt wadding with no shot protectors W W Greener stated there was no "real" advantage of a 10 gauge over a 12 gauge unless one was planning to fire more than 1Ľoz of shot, that the 12 would handle 1Ľ oz about as well as it could be handled.
Along the same lines I also think there would be little Real advantage to going to a larger bore than a 16 for 1oz of shot or larger than a 20 for 7/8oz. With modern plastic, obturating wads with shot cups you could most likely add at least 1/8 oz of shot to those loads. I have had great success in the past with a 20ga firing the old heavy field load of 2˝-1. I do not really expect that a 2" 12 would have been enough more effective to have noticed, unless it just happened to be a better fitting gun which I shot better, but that's not gauge specific.
