Im still not getting the level surface theory. now this trailer has electric actuated brakes so why would it matter if the unit is level or not?
it should just be a signal or not.
with the controllers Ive used they have been adjustable so if you had a light load you could adjust the dial so it brakes less. I remember that controller being on the floor and picking it up to use it and putting it back on the floor.

To simplify the explanation, there is a pendelum in the brake controller that adjust how hard the trailer brakes are applied. When you truck is stopping you are applying forward momentum to the pendelum and it adjust braking force proportionatly.

If you remember your old brake controllor you either had one of the cheap ones that worked off your brake light switch. With these you were either not stopping that trailer or you were locking up the tires, there was no in between. Or you had one of the good ones that tapped into the brake hydraulics themselves and used the truck braking sysytem to control the trailer. These worked great, but a pain to install and they had a habit of leaking. When they leaked your truck brakes were affected even when not hooked up to a trailer. The trailer brakes were also complicated on these, so they weren't a good set up for your weekend homeowner hauler that makes up 90% of the market today.

I understand now.

it makes sense.

so if the controller says it applies force proportional to what is requested it uses the pendulum to sense this.

In a very simplified way of saying it, By George I think you've got it. In real life it's way more complicated then that, but that is what it boils down to. The better controllers are also programmed to accomidate mounting on an angle by adjusting this stystem to match the angle. Don't ask me how they do this. If you notice the lesser models have to be mounted at only very slight angles and some have to be completely level.

yeah the module I used in the past was either on or off. but you could adjust how much the brake was on. so it didn't work as well as the inertia ones