The mirror dip only works if you have the mirror knob turned to left mirror adjust, so put it in the middle when reversing in car parks etc (no kerbs) and use it when required.
Thats what i do with mines
Annoyance I found with it was that the mirror did not always return to the right position after reversing. Occassionaly it would end up giving me a nice view of the sky. Put this down to not having the memory seats option which was a pre-requisite at the time my car was built for the mirror dip facility. That said it is not 100% perfect on my C8 and there it comes as standard - but without the need for memory seats