Hi Doug,
The Groups use the same send for the main mix, so it is purely a routing change and not a new mix send. You therefore need to remove the channels from the LR mix when they are assigned to a group and then assign the group to the LR. This can all be done by having the LR mix selected and using the assign key.
The pan for the input channels when LR is selected will be the same for the group and the pan for the group can be found by pressing the Sel key of the group, the pan encoder will then light up.
To configure your group to be mono or stereo, go to Setup > Mixer Config > Mix Stereo.
I hope this helps!
Alex