I would start with setting it low, and then increasing it so that when
you hit the brake, the trailer pulls back, but gently. Note that
everything depends on how hard you brake also. I have electric brakes
on my trailer. I figured that for empty it should be 1.4, for 1.5-2k lbs
it should be 2 or so, for 4000 lbs it should be 3.4 or so.

i

In other words, just go by feel. I guess i figured that's the only way.

Karl