I can't edit my last post and I wanted to add

My understanding is that you want the gain as high as possible without saturating. X,Y and Z values are in the range -2048 to 2047 so I guess you're looking for something like -1500 to 1500.

I see you don't allow for declination, the difference between magnetic and true north. You can get your local declination from http://www.magnetic-declination.com/

I'm assuming the the X coordinate points North, although now I think of it I can't see why. the only reference I can find is "Arrow indicates direction of magnetic field that generates a positive output reading in Normal Measurement configuration" take from that what you will.

George