Hope this article may help from natural horse supply on yielding from the poll. It may be a solution.
"This is one of the most important but most overlooked things that everyone should be doing with their horse. Yielding at the poll is how you teach your horse to "turn off" or get out of the high headed adrenaline zone area when you want them to. The basic idea is that when the horses head is up high they are in a flight or fight posture. When their head is down, at or below their wither -- they are in the submissive grass eating zone. You can teach your horse to go here when you want, and before you know it that's where they stay. You can teach your horse to be calm and when you get into a situation with too much stimulus all you do is "turn off" your horse. Sounds easy doesn't it!
The poll is the last vertabrea that connects the spine/neck to the head. It's also called the Atlas joint. This is the place that a horse should bend when collected. Most horses are braced at the poll. The easiest way to get through this is to show the horse how to follow a feel. While on the ground, if you use the knot at the bottom of the rope halter to pull down and your hand on top of the horses neck at the poll (just behind the ears). Ask the horse to lower it's head. Immediately when the horse drops its head, release the pressure on the rope. Reward your horse a lot when they are in this position -- head at or below the wither. You will probably have to pull down very hard with the rope halter at first. Most horses brace against pressure and will not release easily. But remember, start with very little pressure and use whatever is necessary to get the job done.
Eventually, all you will have to do is put light pressure with your hand on top of their neck. And even further down the road, you work down their neck to the wither. So that a light pressure on the wither causes the horse to lower it's head into this "turned off" zone. It gets better too. We teach every horse that when we put the rein down on their wither, that they need to release and drop their head. No one ever notices this except us and the horse, but it is wonderful. If we get into a situation that the horse doesn't do well with, we "turn her off".