Hi Jeff. Covermap is specially thinking for a high antennas (12
meters). When you do click on some point in the map (with zoom) the
application calculates the coverage area in consideration of the
terrain elevations.
If you want to position one antenna in the same point that the last
antenna, you should to change some parameter and automatically appear
a “recalculate” button.

I recommended the help section. In this section there are demo videos
and other data like the propagation loss model of the application.

http://www.covermap.es/faq.html