I'm not sure that the calibration settings are uniform from one controller to another. I started with the control wheel completely off and rolled on what I thought might be a minimum setting- maybe a quarter turn. I then got to a safe, open space where I could simulate a "non-panic but serious" stopping situation. (Approaching an intersection at a safe speed when the light suddenly turns.) I was satisfied with my stopping distance, and haven't adjusted it yet. (I take that back- I must have inadvertently rolled the control wheel forward to the point that the trailer wheels locked up with next to no brake pressure. Fortunately this did not occur in a critical spot. I went back to my original setting and everything has been fine.
(2013 RP-177 and 2013 Silverado 1500 with factory tow)