There are so many factors affecting our signals, but we can't tell they are there without expensive test equipment, and the knowledge to use it. I am not sure where you are in the world that you can go out .435 miles (almost half a mile) while you are flying a quad like this, and most of the time you would run out of 5.8GHz video signal long before without a ground station and some real nice antennas, which is just one of the ways "long range" fliers "get out there" like they do. Land and trees and other things degrade the 900MHz signal Crossfire uses just like any other radio wave, but at 900MHz it is much better than say a 2.4GHz control link, but still it can't go through land or a thick forest very well. If you are setup for and watching your LQ from your Crossfire then you can tell if it is a signal issue causing your failsafe, until then it is simply a guess. Vertical mount of both the TX and RX antennas can pose issues with mounting and antennas hitting the ground etc., but will give the best range for a given area and the noise in that area. I have more questions than answers about what really happened to your control link causing you to fall from the air. Good luck and let me know if I can help.