I think that your observation of water is probably spot-on. When it comes which RF frequencies get absorbed, with water the answer is pretty much "yes". Combine

I think that your observation of water is probably spot-on. When it comes which RF frequencies get absorbed, with water the answer is pretty much "yes". Combined with what I'd imagine is some really fun scattering math tossed in, tree cover is a pretty good bet for reducing signal quality, especially if it's more than one.