What's the Deal with Boo Boo?

In Hanna-Barbera's YOGI BEAR cartoons from 1958 and onward, Boo Boo played Yogi's sidekick.  But here's one thing about Boo Boo that has been strange from the very beginning:  his design seems to change from one cartoon to the next.  He might have a round head in a cartoon, and then be blocky in another.  He might have no forehead at all in one segment, and then he'll have a long tall forehead in the next.  The point is this:  early on, the folks at Hanna-Barbara were not terribly concerned about having a consistent model sheet for Boo Boo.  (Nor one for Ranger Smith.)