Tbh, in the film it's supposed to be as if he doesn't have the strap at the back but... you'd be an idiot to think that Adam Driver himself didn't have a strap for it to stay in place, in photo shoots you can literally see the cape solely relying on the strap to keep it in place. but ANYONE trying to disagree and say he flips the cape off so he can't have the strap is dumb as shit, going off of that logic, when he takes his helmet off in TLJ and TFA it removes a full face balaclava and his neck seal so the neck seal and balaclava ain't there, right? WRONG. (Aimed at haters, not dawn)