5.8Ghz is very deceiving in videos.
1. Interference. Its not just trees, but houses with WIFI, and multipath reflections.
2. Power in my experience only helps a little. Think about typical patch.. 12dbm to 15dbm. Now compare power. 100mw 20dbm to 400mw 26dbm.. its only 6dbm. More power often causes more distortions.
3. I rarely fly 400m+ because I dont fly 100m+, and close to ground hard to find Utah desert wide clear space in city.