Inaccurate angle of attack

Hi

I've recently got an R10.

Set up outdoors hitting into net. 10ft net to ball, 6.5ft or so ball to Garmin. I've made a DIY stand with laser level and bubble so I know it's level and the bottom of the garmin legs level with my hitting surface.

I'm always getting good negative angle of attack numbers, as much as I want them to be true I know they are not always that good! I even try to hit fat shots to test it and I still get negative number! Anyone experienced this or got any ideas?

Thanks 

James