Non-aerial factors affecting transmission
Unless you're using your devices in a vacuum, with clear line of sight between aerials the following will have an effect:
- Weather (temperature, humidity, and air pressure),
- Transmission power, bandwidth, spreading factor, and other associated channel factors,
- Number of nodes within reach of the mesh (affects retries consequent duty cycle hit),
- Absorption by materials (with varying degrees attenuation, by material and depth),
- Reflection off surfaces (and channeling through material tunnels, including warm / cold air tunnels commonly present in the atmosphere),
- Diffraction around obstacles (over forests and around corners).
- [Fresnel Zone](They may not have been selected for your given frequency range, tuned or of a quality design.) - Football shape between antennas that must be clear of obstructions or else the signal is attenuated.
Environmental factors
For a bit of light reading on environmental research:
- RF attenuation 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 attenuation 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), and they reflect off surfaces at low angles of incidence. They go through humans without much attenuation; but not brick, stone, or anything with more attenuation than glass / Kevlar. Oh, and don’t sit under an LTE tower and expect it to be plain sailing. RF emissions at adjacent frequencies can interfere at a high enough power.