I think it's also worth pointing out that characters like Tails, Knuckles and Vector technically don't the same muzzle/mouth designs like most other characters. (Knuckles' tapers out into a 'point', Tails has a small canid muzzle of sorts and rarely uses the side mouth anymore, and obviously Vector has a long crocodile snout. I guess you toss in Antoine and Rotor too) All theirs protrudes out enough to where you can't fully see their other cheek in certain 3/4 angles.
I’d say for the most part all Sonic characters have roughly the same type of muzzle, just tweaked/pushed pulled in different ways. If you master the basic muzzle, you’re in good shape for tackling any other arrangement.
it’s also worth mentioning on the mouth placement- ‘cool’ characters get side-mouths (Sonic, Shadow, Rouge usually, etc), ‘cute’ characters get front facing mouths (Amy, Tails, Cream).