So I just recently got into aircraft scanning, and I have a question about the Denver ARTCC radio sites. Based on a cursory review of this map API (Military Comms Map of ARTCC (Air Route Traffic Control Center) Transimitter Locations) it seems that ARTCC radio sites in the Denver-Metro area are not situated atop any of the popular "radio tower mountains" such as Lookout, Squaw, Thorodin et al. Are the ARTCC towers intentionally designed to only cover airspace, such that they can't be easily heard from the ground?