well, locking up the trailer brakes is probably not something desireable in normal operation - but i suspect that if the trailer is brand new and the brakes are brand new - they will require some time seating before you feel the full benefit of the electric braking system... a few long downhill grades where you will be applying the brakes on the tow vehicle anyway to slow down will help with bedding the brake shoes as well as cleaning off any residue or rust that may be on the trailer brakes to begin with.
as i said earlier in this post, i'll manually apply the brakes on the trailer when i am first pulling out of storage with the "oh ****" lever on my P2 controller. this is just for me to 1) test that the brakes are functioning and 2) to physically grind off any rust/debris that has accumulated on the brakes since i parked it from the last trip.
i dont remember what my numerical setting is right now on the controller - the numerical setting is not as important as how it "feels" - if it feels like the brakes are balanced between the tow vehicle and the trailer, that im not either dragging the trailer or pushing the tow vehicle, then thats the setting i go for - to me, the dial could have no numbers on it, it makes no difference, the numbers are meaningless to me as every single application is going to be different - it depends not only on how good your trailer brakes are but how good your tow vehicle brakes are.
my tow vehicle is a V8 HEMI Jeep Commander with EBC performance brake pads and EBC performance slotted and drilled disc brake rotors on all 4 corners - so the big tow vehicles braking is very efficient and consistent. so in my application, i may have the voltage for the trailer brakes set relatively low compared to someone else's vehicle.
in terms of break in for the trailer brakes - i would say 100 miles or so of varied driving, with long consistent braking down grades (which tends to be light application of your vehicle brakes over a longer time) as well as shorter stopping for red lights and stop signs (which tends to be heavier application of your vehicle brakes for a shorter time) should provide the necessary wear and tear to bed the trailer brakes to their optimum.
power setting from trip to trip fluctuated slightly and if i was driving in the mountains for an hour or two, i might even make an on the fly adjustment to get a bit more stoping power from the trailer so the tow vehicle was doing as much work on those downgrades.
i couldnt say that it consistently went in one direction or another - i just would adjust by feel, the road conditions i was currently facing and what felt the most balanced - sometimes that would be a slight adjustment up (more voltage, more brake pressure) and sometimes it would be to adjust down (less voltage, less brake pressure)