Cliff sensor reflector

I bought an AGDA Robotic vacuum cleaner which refused to clean my kitchen floor, backing out of the kitchen as fast as it could, terrified it was going to fall off a cliff.

A search of the net revealed two things>
1. This machine appears to be one of many coming out of a factory in China called Lilin ( http://www.robotvacuumcleaner.cn/ ) and also appears to be the same as the more commonly known brand Roomba.
2. There are many many complaints of Roomba vacuum cleaners going backwards when they mistake some dark colours as a long drop.

I tried some masking tape over the sensor as suggested by many forums but the sensors on this one require a gap to let the light through. Having found that a piece of bent white card sellotaped in place worked I decided to make this piece of plastic to do the job properly. My house is all on one level so I will eventually glue these in place (once the warranty runs out on the cleaner).

If you have the same problem and the same sensors, try t