Unless you're using your devices in a vacuum with clear line of sight between aerials the following will have an affect:
- Weather (temperature, humidity & air pressure),
- Transmission power, spreading and other associated channel factors,
- Number of nodes within reach in the mesh (affects retries consequent duty cycle hit),
- Absorption by materials (with varying degrees attenuation, by material and depth),
- Reflection off surfaces (and channeled through material tunnels, including warm / cold air tunnels commonly present in the atmosphere),
- Diffraction around obstacles (over forests and around corners).
For a bit of light reading on environmental research:
- RF attentuation in vegetation (yes really); if you wander through the woods wondering how your RF is bouncing off leaves dependent on their variety, and wind speed … well you do, now.
- RF attentuation with various building materials.
- This one by ITU again is very detailed in its analysis of the drivers of attenuation (I wasn’t aware that all EMF radiation exhibits reflection / transmission characteristics akin to light hitting a material boundary. So, depending on the angle of incidence, material and the EMF wavelength, it will be reflected and / or transmitted through).
- These RF bands are also made more noisy by adjacent LTE
In summary - wavelengths in Europe fair well in plain sight, curve over not-so-tall obstacles (including trees), reflect of surfaces at low angles of incidence. They go through humans without much attenuation; but not brick or stone or anything much above glass / kevlar. Oh, and don’t sit under an LTE tower and expect it to be plain sailing.