It wasn't a function of the location but the battery was my limiting factor. I think I could have flown at least another 2 miles.You can probably get even more range if you can find an even more isolated spot.
The real limiter is the SN (Signal to Noise ratio). If you have Zero background noise you could probably double that distance. Of course to do that you would probably need to be flying at night over the water and somewhere where no WiFi and other man made signals are present.
It would make for an interesting and expensive experiment.
Rob
Just shows how well this machine is engineered