Good article about what effects the range
Interesting chart on the page and this summary
Physical objects: Trees, masonry, buildings, and other physical structures are some of the most common sources of interference. The density of the materials used in a building’s construction determines the number of walls the RF signal can pass through and still maintain adequate coverage. Concrete and steel walls are particularly difficult for a signal to pass through. These structures will weaken or at times completely prevent wireless signals.
Radio frequency interference: Wireless technologies such as 802.11b/g use an RF range of 2.4GHz, and so do many other devices, such as cordless phones, microwaves, and so on. Devices that share the channel can cause noise and weaken the signals.
Electrical interference: Electrical interference comes from devices such as computers, refrigerators, fans, lighting fixtures, or any other motorized devices. The impact that electrical interference has on the signal depends on the proximity of the electrical device to the wireless access point. Advances in wireless technologies and in electrical devices have reduced the impact that these types of devices have on wireless transmissions.
Environmental factors: Weather conditions can have a huge impact on wireless signal integrity. Lightning, for example, can cause electrical interference, and fog can weaken signals as they pass through.
Lots more testing can be done even before Particle gets full mesh connectivity going.
I need to do my line of sight tests on a foggy day and users should expect complete collapse of there outdoor systems during a thunder storm.
My update is that I am only really interested in the line of sight studies. Too many ways that the data can get messed up inside a building. I will try testing glass today. One cool idea is; could a mirror or sheet of aluminum foil strategically placed inside a building reflect a signal around a major RF blocker!