He may still walk around a bit later if he changes his mind. When mine was new he settled for a couple of days and I thought to myself that he had found his spot, and then he took off again. Gradually working his way behind the rock pile, up the back glass, around the overflow, and finally stayed put on the glass of the left side of the tank just to irritate me.
I was on pins and needles watching him walk around the overflow.
Your nem looks like a good nem and plenty large enough for your maroon. Maroons can really beat up a nem, so keep a good eye on him and be prepared to separate him from the clown if he becomes too aggressive.
One of the other people around here has a maroon named FeeBee and she pretty much loved a RBTA to death. I can't think of who it is right now, but I know he's around here someplace.