A true gag bit works the opposite has previously explained. (Maddie may have been talking about a Dutch gag but despite the name is not considered a true gag bit) A gag puts pressure on the lips when the reins are pulled which causes the horse to pull his head up. The key to your answer is correct training. You are wanting to poll pressure to help with an outline, right? To get a "proper" outline or headset you need to train your horse from the back end forward. Throwing a bit on or using gimmicks such as draw reins will not solve the problem. These are only quick fixes. I suggest you stick with your current bit or something softer and work with a trainer to achieve what you want.
Hope this helps,
I would recomend a gag. It attaches to the cheek pieces and puts pressure on the pole if they like to go around the ring with her head up in the air. This just gets them to bring their head down so they can see where they're going.