The comments thus far are for the most part valid, and as you have already found out there isn’t much practical difference. However one point was overlooked. In addition to a little larger area than a 12-6, it will also have a little greater pitch. The pitch of a propeller varies from pretty steep near the hub to much flatter toward the tip. This is so that when moving through the air, the blade angle of attack at each radius remains close to the same. By convention, the specified pitch is the pitch at a specific radius (usually 75%). By shortening the propeller you cut away some of the flatter pitch, and the pitch at 75% of the new radius is a little greater than that point on an original 12-6 prop. I suspect as much or more of the additional load on the engine comes from this pitch increase as from the increased area.