I understand the principle of moving it back for more room... How does it look?

The plate looks just fine, as shown. I have mine in the 1 1/2" position, and the only way you can tell is that you can see a bit behind the seat because the flap thingy on the TP backrest is not quite thick enough, but it's really not a big deal. At 2 1/2" back, that would be a little more obvious. If it bothered you enough, you could always fix it by taking the backrest off and having the flap thing re-done to be a little bit longer/thicker.
Makes getting the seat screw off a lot easier too, and the speaker pods don't touch the sides of the seat any longer.
Where you put it is dependent on the size of your BSR and body type...1.5" seems to be perfect for mine...her butt is on the whole seat now, where before the back 1.5" was not even being used. At 1.5" the TP lumbar support appears to be vertically aligned with the back of the seat. With the new lumbar support in the backrest, there is DEFINITELY less room for the BSR than was the case on my '06 SEUC.