Jeff,
Have you checked to see if 0 is actually power off (no power going to the antenna). I am told that it is not but rather it attenuates the signal enough to pretty much cause the same effect.
The Sensar Pro can either amplify or attenuate a signal from the BatWing. 10 is a setting that is neither amplifing nor attenuating. Increasing the gain from 10 to 15 would be a 5dB gain so the max gain would be a setting of 20 or 10dB gain. Anything less than 10 would attenuate the incoming signal but it may not be quite as linear.