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Small changes in the simulator in physical location or height are generally irrelevant due to the limited resolution, both vertically and in horizontal (X, Y) space, of the digital data that represents the terrain model.

As the disclaimer on TVFool clearly states, "Please understand that this is a simulation and can only be treated as a rough approximation. Reception at your location is affected by many factors such as multipath, antenna gain, receiver sensitivity, buildings, and trees - which are not taken into account. Your mileage may vary."

After a certain point, practical experience has to take over from mere numbers since the numbers are of limited accuracy. I've learned (the hard way) that putting the antenna where its odds are the best is usually the most direct path to success. Shortcuts done for expediency or convenience too often will result in compromised results.