PtMP 3.5 or 3.65 services should never be implemented with non line of sight, or through trees. In a typical TDD airtime system, no matter what it is, one client out of twenty on an AP radio with poor signal (let's say, -77 on both chains) will consume more air time and drag down the performance of the entire AP. There's a reason why all the deployment guides for modern WISP PTMP radios are quite insistent on true clear fresnel zone between CPE radio and AP.

But if I had a dollar for every shoddy 802.16d-2004 or 802.16e based WISP trying to shoot through thick foliage or even install CPEs inside peoples' windows....

I think the other issue is that demand increases the most when it’s raining, just when supply is the lowest, further crushing any weak systems.

both contain water.

"contains water" wouldn't normally be enough to suggest something is weather, but this is Britain so it's actually a reasonable comment.