Diff board installed, situation much improved :-)
Think of the projection zone window as a screen...
If the image fills the screen, and you move the image to the left it will start to squash the left hand side of the image... So to move the image within the zone, you have to reduce the size of the image...
To move an image that is the full size of the zone, you would need to move the physical projector to hit the screen...
Mark