I recently mounted a RHS mirror; already had the LHS. The few 113s I've seen all had both mirrors set back the same distance from the front.
After reading postings here about placement of the mirror, I decided the RHS should be placed further back from the front. I decided on one inch. Using the new rubber gasket as a template, I marked the centers of the holes. I started with a very small drill, because it wouldn't drift off the mark, and then finished with the proper size.
After putting the new mirror on, I found I had to bend the reinforcing metal inside the door in order to get the nuts on, but that wasn't a big problem, and nothing inside the door was affected by this bending.
As for vision, I wish I had set the mirror 1.5 inches back. I can use the mirror as it is now, but part of it is obscured by the front window post. It would take a very critical eye to tell the mirrors are not placed equally, and going to 1.5 inches would not be noticable, either.
Also, the mirror will not affect a passenger's vision, regardless of the placement. That was a concern I had, too.
Both mirrors are placed the same distance out from the window. I don't recall that measurement, but others have given it here.
Joe