There are two scans with the Sensar Pro.. First it scans.. It scans for both the strongest signal (Which it displays) and for all detectable signals (Which you get with a different menu choice) But this in no way affects the TV, just makes aiming the thing easier.
The final scan is with the RECEIVER (TV or Digital Adapter) And there I normally scan at 10, which suspect is unity gain, but can't be sure since I did not do a "side by side" and then up the gain if needed.
Of course, after the first few times in any given park, ,I learn to preset. For example where I am now 20 works great.. Give me a week and a halfl and 10-15 may be better. (Too much signal/gain is as bad as too little it turns out)./