All you need are some decent rear facing reflectives and they will trigger given the right speed.
Indeed, I think the reflectives thing is a red herring, or coincidence.Not necessarily the case. On a FNRttC I've gone down Ditchling Road into Brighton wearing my Night Vision jacket, which is liberally covered in reflectives on the rear and not triggered the speed camera at 38 mph. I was matching the speed of a tandem further in front of me which did trigger the camera.
One day, my Garmin claimed I reached mach 3 or thereabouts.
35.4 mph.57 km /hr. Not sure what that is in real money !