Being a do-it-first then read the manual kinda guy....
I set the gain in the middle and felt how things worked.
Too much gain and the trailer's brakes pull the truck to a stop. Too little and the truck's brakes are carrying too much of the braking load.
With that, I have found a setting that works great on the Interstates. I've found that bringing the trailer's brakes in sooner helps on local streets. But, since so little of our trip is on local streets, I don't re-adjust for those short pieces.
Then, once we get to the private dirt road, I remove the brake controller. The idiosyncrasies of electric brakes left some nasty gouges a few years back. At very low speeds the truck's brakes are more than adequate.
So, my advice is "Get a feel for your rig" and then "Adjust for what is comfortable".
I know I can feel when the trailer's brakes have ramped up and are doing more braking than needed.
TT 2015 19RD "TheJayco"
TV 2003 F-350 "Montblanc" - Housebroken chore truck
Sitting in The Cheap Seats.
And proud of it!