What mkirsch is saying is correct. The IBC works off of the hydraulic brake pressure. The harder you hit the brakes the higher the gain on the IBC. Kinda of like an automatic boost. Unfortunately it dosen't work as well as an aftermarket. This is why you can get more gain by manually hitting the trailer brakes. Being firmer on the brake and then letting off would be more effective than "riding" the brake as was mentioned earlier. Also following APT's advice would also give you more braking. When I got my new truck with an IBC I had to go from 2-2.5 on my Kyosho to 7-7.5 on the IBC.
