GF1 is absolutely right. RCC, your light 12s aren't much different in breadth than your 16s because of variation in chamber wall thickness that's not generally seen in barrel wall thickness along the length of the barrels to the muzzles. Those 16s look to have thicker chamber walls than that 12. It's along the barrel length that the slimmer 16 ga. profile is easily seen, more consistently reflecting the difference in bore diameter. Even if a 16 has a thick breech, unless the entire barrel is overly heavy the trimmer profile will be apparent nearer the muzzles.

I've never heard a discussion on the aesthetics of chamber wall thickness.

Jay