I had a kinda funny thought I just wanted to put into words. The whole Mirror realm/shadow replication thing has been my thing for awhile now in the DF. I've researched it from various angles and mythos. That part of what N does is find that mirror and/or use mirrors.
Anyway remembering the 'son of the chief Physician' idea and connecting the references, mainly from MS hanging around MW's cottage, Mort's Guardian's giving stability to the Insane ghosts(which i'd point out for my own reasons basically gave them a sanctum/home to live) and in DR's make up as well.
Long have I thought of TWC the spiritus mundi of reality, the one who dreams up it's existence/defines it's will(in this way reality is kinda just HIS sanctum)
Basically, Mac is 'out' and does not interfere, though he's actually inside reality... Nemesis is actively interfering though she is 'outside' reality. I think he surrounds himself in Mirrors as a way of balance for that fact. He's surrounded by Nemesis's medium in a place in a sort of wonky way for balance... anyway, had to say it