In your case use antenna height only to avoid trees and buildings. You will probably find a good location at a modest height or even a lower mounting point. The key is to find a spot with open ground in front of the antenna. When you test signal strengths, start with a channel in the upper 20's or low 30's and then verify that upper and lower channels work OK. Lower mounting locations are more likely to work on all channels. Read
www.hdtvprimer.com/antennas/siting.html for an explanation.