Some of my bodygrips have 2 notches, some have 3.
A marten trapper told me once that the end notch was more sensitive. Without having very accurate scales, it would be hard to measure the difference in "trigger pull." I also agree that it's going to be a very slight difference between notch #1, 2 or 3.
I also use the end notch, probably the biggest reason being, it gives the trap a little bit wider "stance". And it also gives me a place to wedge a limb or pole or stake through the spring, and into the top corner(s) of the trap.
Talking about the trap dog, I think we talked about bodygrip adjustment before? All of my bodygrip dogs were "machine stamped", and I take a chainsaw file and square-up the notch that I'm going to use.
It only takes 3 or 4 strokes with a good file, and once the trap is set, the dog won't wiggle around on the trigger. You can kind of feel it snap into place.