Used to believe that head/neck pressure was ‘the’ central principle in domination, but think about it, if you can’t dominate the bottom players legs and torso with your gravity powered legs and torso, how are you going to get to the head/neck in the first place?
Rickson Gracie covering above principle @ 0:44-8:51:
To the mirco-adjusting, the idea there is the subtle shifting of our weight to counter a training partners attempts to turn in or away from us. This is more subtle than Rickson switching his hips above, and invisible in that its affects are felt rather than seen.
To illustrate, referencing the Rickson footage again, based on his arm position if the opponent tried to turn in, he would drive slightly into the far side shoulder. If they tried to turn away he would sag back slightly. In both cases I’d probably add a bit of arm pressure at the shoulder or leg as well, but like the idea of letting our body-weight account for 80-90% of the position with our arms being a compliment.