The shots below show my settings in the DJI Naza Assistant software for the X, Y & Z co-ordinates and what that translates to on the Quad. The first time I flew with the GPS, I didn't bother to set any parameters and GPS mode wasn't very good. As soon as I activated it, the quad would bank left and drift quickly until I re-engaged attitude mode.
I made three changes before the next flight. 1. Mount the GPS on the stick provided, 2. Point the arrow on the GPS towards the front and 3. Enter the co-ordinates in the software configuration. After another test flight, the GPS holds position pretty well. What I don't know is what had the most effect (the mount, direction or co-ordinates). I'm hoping it's the co-ordinates in the software because I'd prefer not to use the stick mount because it makes it bulkier to pack and more prone to damage on a hard landing. I think I'll try going back to double sided foam tape and mount it directly to an arm.
The pictures below show these settings X = -4cm, Y=4cm and Z=-9cm and what they look like in the real world.