Back a while ago, before Mavic came out, back on the
Phantom 4 forum, I remember a radio expert guy explaining some technical details about DJI's radio communication methodology.
I recall that 2.4 and 5 GHz radio is very close to microwave (just like the oven).
and because of that nature, it is very poor dealing with water.
the water would change that radio energy into heat and the signal would fade/weaken out.
it's extremely sensitive to trees (liquid within). the brick building after rain storm would def have significant impact on 2.4 and 5 GHz performance.
obviously, open area over water would have less obstruction than urban or forrest environment.
But more than anything, the humidity in the air (even if it is unobstructed) impacts the radio comm incredibly..
that's what I recall from that forum posting.
and then he went into the science of different types of antennas and the orientation of the antennas, etc... I'll see if I can find the article and post the link, if I locate it.