Yeah perhaps it belonged to Stevie Wonder once?
The reasoning behind thinking the front sensors engaged when selecting reverse was. as I stated originally, when parking between two cars. You first reverse into a spot, then select drive and the front sensors would beep to warn you from hitting the car in front. This, I understand is how the majority of vehicles engage their front parking sensors when both front and rears are fitted, alternatively there can be a switch.
Just trying to find out how ours are meant to work as they appear to be not working.