A license plate in that position won't comply with the laws in most states. Unless you like playing "chicken" with the Law.....the plate shouldn't be hidden behind the tire. The photo you listed is at an angle that shows the plate - but when you have the bike upright and your weight on the seat.....and the Officer is 20 feet behind the bike inside a Patrol Car......all the Officer is going to see is the top of the back tire and a bit of license plate on either side of the tire.
When I was deciding what to do with my plate, I went and talked to a few of the Police Officers at the small towns I work for. The unanimous comment was the plate needed to be easily visible, it needed to be horizontal, and it needed to be lit. (Some states allow vertical plates).
I don't like the plate on the back of the seat/fender...it ruins the smooth lines and rubbing the tire can be a problem. I toyed with the idea of putting the plate up at the frame like you posted - but I just want to ride and not be fussin' with the Police on a continual basis. I finally settled on a side mount as a way to help hide the weird shock offset that is required by the belt drive.