The topic of “why doesn’t my antenna work?” or “which is the best antenna” has come up several times on this forum. Many have reported that antennas are “voodoo” or just plain magic. Not quite. The subject is complex, and outside of carefully controlled conditions (such as an RF shield room), and the variables can never be totally accounted. I found a couple of pretty good articles that explain antenna theory basics. These articles can help a user to choose and locate an antenna.
The first article is from Harvard, and it discusses the way that radio frequency waves (RF) propogate, and the major ways in which the RF is attenuated. Warning: this article uses math! http://people.seas.harvard.edu/~jones/es151/prop_models/propagation.html
The second article is about multipath in RF propagation. It focuses more on WiFi and cellular radio, but the principles are universal (e.g., the physics is the same). This one is less heavy on the math, and instead uses text to explain. http://www.radio-electronics.com/info/propagation/multipath/multipath-propagation-basics-tutorial.php