Sorry guys I should have mentioned that I resolved this with the help of technical support.
It turns out the issue I was having was to do with the fact I wasn’t using the “Main” bus. I had set the Main bus to “None” because I was using the Matrix for all my speaker outputs. However if you do not have the Main bus set to LR then the panning of a mono input to a stereo group does not function and remains panned centre.
So basically I loose a bus I’m not using just to allow me to pan the way I want.