The RX400H has a bad design for the rego plate. The backing only supports the top half of the plate. This is a very annoying issue as I have had to replace my front plate twice due to parking knocks that have cracked the plate. This can be an MOT fail.
So to mitigate my next car park knock I have super glued my new plate to the old one as well as the 2 screws that were already in place. I turned the old one upside down so the crack is up. Now, hopefully, my new plate can withstand a little more impact...
I hope this helps!