The trees should have more impact on 40 (UHF) than on 11 (VHF high). 40 is also rather far off axis from southwest. All antennas are directional to some degree, and the better antennas are typically very directional.
Indoors antennas are most suitable for urban environments where local signals are very strong and transmitters are nearby. Any chance that you could move your antenna up onto the roof into the clear air? Even then if you are aiming through trees, you may have trouble. Look here at "Trees and UHF."
http://www.hdtvprimer.com/antennas/siting.html