Just my 2 cents worth, Wave propagation is highly dependant on the frequency. The way that wireless networks work are no different than the way that any other wirless system (broadcast radio, microwave, Radar, etc) works. Another factor of propagation is the matter of which the magnetic waves are trying to penetrate. It is obvious that if the waves are trying to go through a conductor, the instance of absorbtion or reflection is greater than that of a non-conductor. However, as the frequency goes up the level of absorbtion also goes up with most materials; wood being one of them. As one gets closer to the microwave spectrum, the non-conductive objects have more of an affect on the wave propagation. So, having your tranceiver antenna in a line of sight configuration would be best. This is almost always impractical, however. The good news is that packet technology affords us a "not so good" signal since it is self correcting. Your LAN may get a little slower but the packets should still eventually still get there. The exception to that would be excessive delays, which would cause timeouts and dropped packets.
In a nutshell, try to keep your transceievr antenna(s) as unobstruced as possible to the nodes you wish to communicate with. We find that many (MANY!
problems are caused by bad placement of the antennas and higher expectations of the signal quality.