I wonder if he is hard in the mouth because when he is resistant, you meet his resistance and the two of you spend too much time in the place where he is pulling and you are too, and you're in a stalemate, until somebody gives (and is it him or you?)
My recommendation would be to apply the rein, say for a turn or a stop, and if he leans on it or braces against it, you meet that brace but you add an ounce more so that you aren't stuck in a stalemate. He must give. And it can get uglier before it gets lighter. But once he gives you give a big release.
He should start to give sooner and sooner. But you can't just meet his pull with the same amount, you must exceed him , . . . For a bit. If he pulls harder, then you meet and exceed. Also, you can add more bend and more lift to the rein. All these things break out the stalemate.
Soon, he will give to very little pressure, as long as you give a big release and not hang on his mouth.
Yeah, that's another thing that helps build softness; when you are just standing there on his back, be sure you have a real soft drape in the reins. Try to find times when you can drop the reins to be really loose, so that there are times when they are on and times when they are off, which builds the horse's sensitivity to them ( or at least doesnt' dull him out to them).
Whenever you come to a halt, don't release the rein until your horse stops AND comes off the rein. So, you stop your hands and body, saying "halt" and when he does, don't give your hand back to him until he rocks back or even takes a step back and lifts his head up and off the bit, carrhying his own head instead of leaning on the bit , waiting until you take the brake off so he can plow forward. Does that sound familiar?
He is hard in the mouth:
1. Because we do have our stalemates. I have a hard time distiguishing between applying pressure and pulling on him.
2. He's an ex-header. The people who had him before knew only to jerk when they wanted to stop. All he really knew when I got him was left, right, back, and foward. He could barely flex or break at the poll, had no brakes unless you jerked so hard you'd link the bit would hit him in the eye and had no respect for me or the bit.
Now that I have him, he flexes left, right, and at the poll. He collects at a walk, is learning how to neck rein, has a good stop, and a back up.
I just want him to have the least amount of contact with the bit as possible. I realize it is after all in his mouth but I don't want him to brace against or learn to lean on it.
I guess my thing is that I don't want to have to pull to hard on him.
When in our stalemates, should I continue applying pressure when he fights? Kind of bring him into my leg when I use the rein? I don't want to crank him head to where he's at my stirrup. Then when he does bend and gives into the pressure, just let the rein slack and reward him? I get the idea of what you are saying, I just want to make sure that I would be able to do it right.