In my experience, the Parelli method is more for the handler than the horse. In the Porcupine Game, the issue is: Touch. Does your horse even recognize the aid? It's important not to get this confused with the non-touching aid, because people DO touch thier horses and expect them to yield AWAY from the touch. Anyway, the beginner games are fun, I think, because they make you think about every tiny little bitty thing that's going on. I think it's really helpful for the majority of beginners.
In the forehand-yield, from what I've seen (I'm a Parelli auditor, not a real student) the focus IS on the front of the horse, and trying to maneuver, or get control, of this part of the horse, without the horse taking control (in a very small way) and moving some other part of his body. Probably a totally worthless thing to do, but interesting on the human's part: is it possible? And while you do these things, you and the horse are getting to know each other better.
Once someone asked if the method would work well in their school (for at-risk kids) and the answer was, it's hard unless every student was assigned a particular horse, for that student alone. At the beginning at least, it's a one-on-one relationship.
But I don't like it that the method of moving the horse's forhand changed somewhere along the line, so that what I first saw, was quite different from the last clinic I audited a few years ago. One of the weaknesses of the P system is that they keep changing things; and really, no one seems to know why.