Several other reviewers mentioned the size of this "one size fits all" cap.  They're entirely correct.  I have a head size that would normally be classified as XL (motorcycle helmets, etc).  This cap fits loose as a bucket on my head, and the back side of it is just ginormous.  Since it's not worth the effort to return it, I've tried temporarily to get it to fit by rolling under some of the back of the hat under along with the headband (kind of like how my wife rolls her shirtsleeves' hem under a time or two).  It shortens the "back top" of the hat by about 1.5" or so, fitting my head more adequately.

It worked well enough that I'll make this a permanent fix by running a stitch through it to keep it in place.  Looks much better this way and fits just about perfectly.