I use the same set-up and haven't had an issue. Although I do not have the light to tell me the Jk is slowing down I can feel it. When I first got my system it would not activate. Their tech department had me push the plunger in a few times using a 2 by 4 to break loose any debris or weld/paint that may have been inside, it worked. Is your hitch sliding in and out ok. Could there possibly be some rust inside. The cable is adjusted ok?
As you know the whole idea behind this product is the weight of the vehicle pushing against the hitch (surge brakes) At an angle it seems like less force is being pushed directly against the hitch, maybe check that the lever is sliding completely in and out without restriction. How long have you been using this system.