I measure a standard cover plate as being a tad more than 4-3/8" high. The 4-1/4" you spec for the routed-out area is pushing right to the hairy edge of that. I'd feel more comfortable with 4-1/8" there.
Also, found the note, 'Optional 1/8"+ routed area', to be unclear. (As in, I couldn't figure out what the heck you were talking about.) Now that I've figured out what you were talking about, the notes make sense. But I had a hard time getting there from the notes. (I guess I saying that I found it confusing, but I don't know how to state it more clearly.)
