Thanks to everyone who replied, some useful advice & ideas.

When I was last on my bike I watched where I placed my hands, because I move my hands around a lot, I really do use all the bars, no matter where a mirror is anchored (on the grip) it'll be in the way & a compromise unless it's fixed centrally.

I did see a photo (can't find it now) of this set up, mirror fixed centrally & positioned so the rider looked through the bars to see behind, Im going to try for this.