I have a thoroughbred who is currently eventing at beg novice. He has a parrot mouth which is not that bad, prob only about 2cm off from where it should be. But his tongue sticks out without a flash, and I'm having a very hard time getting him to soften. I'm currently just riding him in a plain d ring snaffle. It does the trick in cross country, but it dressage and stadium he's just really stiff to my hands. He gets adjusted all the time, and his neck and back are very well stretched out, he just doesn't want to do it.
I need some suggestions on a bit to help soften his mouth. He's not speedy in the least bit though.