Yes. Just work on one thing at a time. When you get good going straight then you can work on lowering the head. That's what CA says. Otherwise the horse gets too confused. When doing too many things at once. Ya know? Posted via Mobile Device
I think the exercise at this point is just focusing on getting there in a straight line and having clear intentions of where you want to go, instead of just moseying around the arena not sure of where you truly want to ride. If he gets fussy when you arrive at each post, just ignore it for now. Once you've mastered the exercise and your horse is listening to where your mind and body is telling him to go, then you can ask for a bit more by having him remain in a nice frame from point to point. :)
Are you talking about the cruising exercise, or the follow the rail exercise? I think in either one, as long as he is going in the gait you want, you basically leave him be, and only hold him responsible for his gait. Obviously follow the rail you would also hold him responsible for maintaining the position on the rail as well, but basically you only guide him when you need to and stay out of his way for the rest of the time.