(I try to avoid "difficult" horses and prefer horses that are forgiving and like me
)
However, this is the theory that comes to mind IMO:
I think the basic thing is the bond that horses naturally develop with their companions. They want a bond, with friends and with the herd.
A) If a horse is so uninterested that they won't interact, one thing to do is the "walking down" from behind (Zone 5 in PNH, also a native technique, also Carolyn Resnick uses it).
If they look at you, you reward by releasing your "pressure" (take your eyes and energy away from them). This builds toward them actually facing you. If you are so uninteresting that they ignore you, get in range and slap the ground, influence the air/energy, or pop them on the butt (not with a lunge whip - that is too painful). That made you more interesting!
If you are doing this with an aggressive or very dominant horse, don't be in range of retaliation - outside the fence would be safer.
What you have to be able to do is read the horse - them looking at you can be very, very subtle - most people would miss it which would miss the opportunity.
Then your body movements and postures will very subtly influence the horse, you have to know what your body is saying (i.e. shoulder may be blocking a direction). Or are you looking at their head, when possibly looking at their hip or tail might be what you want? (The best way through this is "the horse is your teacher" - when you do something, what does your horse do? - that is your influence.)
I've been working a lot at liberty in the last year, which is quite interesting. My mini would usually rather eat when grass is available (although I've fixed that somewhat) and will scream with rage when I put pressure on (even when only slapping the ground she takes it as a threat). A round pen can be too confining - too much pressure too fast. In a paddock or smaller field, there is room for moving around.
B) If the horse puts his butt to you and will not look at you, one way to gain interest is to put yourself first in one eye - when you get a glance or a look, then put yourself (staying in same area behind the horse) in the other eye. Each time you get the glance, then the turn of the head, you would first turn away (take pressure off). You would go from eye to eye. Sometimes they won't allow you in the other eye, so you have to persist until you can get there. Eventually they will start to turn toward you - you have become interesting to them.
C) An undemanding way of creating the bond of companionship with a horse is just to spend time in his presence without having any agenda. PNH calls it Undemanding time, Carolyn Resnick calls it Sharing Territory. It takes patience to do that, but pays off big time.
IMO the most important thing is learning how to read the horse's smallest indications, and learning what your own indications (small or large, depending on your skill level) create in the horse.
I'm not a teacher and people don't pay much attention to me, but I watch people (even myself) and their aids are far too heavy.
People often say a horse can feel a fly land on them (or just flying above the hair). I say humans can feel a hair fall on their skin - at least I can, so I assume others can. If the horse can feel the lightest touch, and humans can feel it, why not take advantage?
My riding horse that I recently sold sometimes (when I was not sloppy) would follow the direction of my eyes, because that subtly influences my own balance and muscles. My previous horse could be influenced by my thought, because that apparently affected my body balance and muscles, which he felt.
I think in driving, if you have subtle contact on the reins, then the change in direction in your eyes would affect the feel on the reins. That is unless you have developed a horse that only responds to a heavy feel.
Parelli uses the 4 phases of feel - phase one as light as touching the hair.
IMO a true phase one is thought. Ray Hunt said to visualize first what you want.
Well I could blather on, hope it is in line with what you were mentioning. However my sheep and goats are on the lawn so I have to go.