In ESB there are two styles of armor worn by Prowse. One has the shoulder bells underneath the chest armor (like in ANH), and the other has them mounted at the edges of the chest armor (like in ROTJ). When mounted at the edges, it makes his silhouette broader at the shoulders.
Because I wanted the versatility of being able to match any screen shot, promo still, etc.. I had to have both versions for my ESB display.
Of course, only one set of armor can be displayed on the mannequin at any given time, so I decided to make a bust display for whichever set is not in use.
There's just something about seeing that glossy armor exposed without the cape hiding it.