That's what's important, is making sure the mouth is hinged well enough; I've often found that with puppets, the way the mouth is hinged can make or break the entire thing (Don Sahlin wasn't kidding when he said the mouthplate is essentially the foundation for the whole puppet), and improperly hinged mouths can sometimes result in the skull naturally flopping back more than it should - even if you try your hardest to keep the skull still with your four fingers. Same problem could be said for mouths that are too small or too tight; I had an experience eleven years ago when I was given a puppet to perform that must have been designed for child's play, because my hand barely fit into the thing, and the mouth was only big enough to fit the tips of my fingers and thumb into - not my best manipulation work, but at least the kids got a big kick out of the character, which is what really mattered.