As someone who has a perennial problem with this, it's interesting to see the different positions owners have used for their rear registration plates.
I notice in Allen's picture that although his plate is hung from the top of the luggage rack the number plate light is still in its standard position below the bumper. The plate in Richard's picture is above the bumper but similarly not illuminated. Neither would get through a British M.O.T.
In order to meet the test requirements of visibility, I annually remove my back registration plate and remount it on a bracket that lowers it by a few inches. Digimap's appears to be in this position but I find in general use it has a high risk of grounding, particularly when reversing off of my sloping drive.
I have yet to work out why this is a problem specific to that era of 4-seaters.
~iw
Ian I do scrape both the rear and front plate, interestingly in my thread on tyres I noticed a lot of people are talking 16" tyres on their cars, I checked mine and found I have 15" and now I am not sure what is standard.