I am not home - and cannot find a photo of my bathroom. So, I will describe what I did.

The alcove for my vanity is just shy of 83" long. I had the vanity custom made to fit the alcove - it was two all drawer pieces (+ barely floats off the floor with under lighting).

I used two mirrors + three sconces. The mirrors are 24" w x 36" h. My total width of space for mirrors and sconces = 82.875" - 48" (width of two mirrors) = 34.875/3 sconces = 11.625" total area for each sconce. I was able to have my sinks where I wanted them (centered under each mirror) since I had basically two vanities made that were the same exact size = half of the space in the alcove - a little bit of filler on each end in order for drawers to operate correctly + have the vanity scribed to the wall.

I had my electrician wire for each sconce at 66" off floor + centered in the space between the left wall of alcove and left edge of left mirror + in the center between both mirror edges + centered in the space between the right wall of alcove and the right end of the right mirror.

My sconces are not wide - they are on the thinner side vs. the wider side. I can't remember right now how wide the base against the wall is - but 11.625" was enough space so that they have enough space from the walls + the edges of the mirrors.

I won't be home for two weeks - but maybe my daughter can run by and take a photo. I hope the above make sense.

FYI - Initially, I drew everything out on graph paper to make sure that it worked. Later, used blue tape to outline stuff on the actual wall in order to see it before the electrical sockets (I can't think of the right word currently - brain freeze!) for the sconces were installed.