I keep reading that Chaplin had short arms (at least proportionally). I have never noticed this before (like I can't really tell that he had a large head for his body...). But lately I have seen so many photos of him where he is trying to cross his arms and doesn't quite make it. Kind of funny - like he is a little boy trying to look grown up around the adults. Ha!
To me, Charlie's head doesn't look large for his body, in most photos anyway. But the scenes in THE CURE where he is wearing a bathing suit, I think its noticeably large. Maybe it's because his hair is kind of bushy as well. But it was something he was self-conscious about. As far as the arm-folding. In almost every photo, especially where he is posing with another person or a group, his arms are folded.
I think his expansive forehead also helped to make his head look larger. The arm-folding, especially in the group photos, strikes me as the body language of a socially awkward individual. He was actually pretty shy.