I'm not sure in that instance, but you're on the right tract if there is a solve. I know that some female heads can have their bald head push through a hat.
Narrow shoulders is probably not what you're shooting for.
I've tried several different combinations, but it never seems to be quite right. I suspect that if I was wearing a tight chest costume piece instead of a robe, it would minimize the problem, but it's not the look I want for the character. 
I even tried changing the robe color to match the cloak color, but the texture of the robe is still noticablely different from the cloak and looks quite obvious.
I'm going to be doing some more experimenting today, but just playing around with the power customization, I also noticed that the cape very badly clips with the body during the use of the Storm Summoning power "Thunder Clap" (and I suspect the same would hold true for any similiarly animated power.)
Unfortunately, until and unless CoX adds a strong wireframe to the capes, I think there's always going to be clipping problems with certain powers and with running.
Okay, rolling a new character and I decide to give him the high collar cape (because hey, it's a magic origin character and they look cool), and I notice whenever I run, I can see the robe underneath the cape "clipping through" the shoulders of the cape.
Is there any combination of body settings (physique, chest, shoulders, etc.) that eliminates this or minimizes it to where it's not very noticeable, or should I just make the robe color the same color as the cape so I can't tell when it's happening?