Just heard the following:
Most hand held speed guns need to flat or near flat surface to get an accurate reading, therefore the operators are told to point the gun at the vehicle number plate for the best reading. Therefore if you fit your plate angles either up or down then this will reflect the beam at aunfavourable angle and the operator will have to target elsewhere on the vehicle/will take longer to get a reading.
ie. you will get a few seconds extra to slow down before they can get a reading.
Anyone verify this?