Sone wiper arms are located by a taper instead of a spline.
When the retaining nut is loosened, the grip of the taper can be broken, and the arm repositioned wherever you like.
The dealer hadn't checked our Renault's rear wiper, which turned itself round and concentrated on wiping the rear number plate.
Slackening the nut, a judicious tap on the end of the shaft to break the grip of the taper, repositioning the arm and re-tightening the nut taught it better manners in less time than it's taken to write this.