Regarding the effect of altitude on the strength of the transmission signal, this is just speculation, using what seems to me to be sound logic, but it might not be. I welcome being shown where I'm wrong if I'm mistaken.
The conclusion of my self-supposedly-logical thinking is that altitude does increase signal strength, and here are the steps by which I came up with that speculative conclusion:
1. Since a lesser amount of signal still gets through even when a solid barrier exists between the aircraft and the remote control, some of the radio frequency signals are transmitted by indirect, non-linear paths, bouncing off of other objects.
2. The more altitude the aircraft has, the more of these indirect signals are available to the receivers on the remote control and on the aircraft.
3. The maximum amount of signal is when the aircraft is directly above the remote control.
Edit: (3a. Hmmm... except that if the antenna is straight up, it's parallel to the legs of the aircraft but it's not "facing" the aircraft... I didn't think of that... might shoot the whole theory.)
4. The greater the number of degrees above the horizon that the aircraft is, the more available signal there is.
5. The greater the altitude of the aircraft, the greater the number of degrees it is above the horizon.
Edit: (5a. I'm amending the theory, due to 3a, to say that 45 degrees above the horizon is optimal... where altitude and distance are equal.)
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In other news, I've flown my
P4P enough now to have reached the evidence-based conclusion that it has significantly greater range than any of the Phantoms I've flown previously from my tree-surrounded location, including P2V, P2VP, and P3P. The range I get with the
P4P is 50-60% further than I ever got with my P3P, which has the second-greatest amount of range.