My Tekonsha Brake Control Quick Reference Card suggests setting the knob at 12 o'clock, travel at 25 mph and apply the manual slide switch. If the brakes lock up turn the knob toward 8 o'clock; if not enough stopping power turn toward 5 o'clock.
Somewhere I read that the combination of vehicle and trailer should stop in the same time/distance as the vehicle alone and the Controller should be adjusted accordingly.
Hope this helps.

Dick_B