You have a very cute horse!
You look like you are a bit on the stiff side, and this is reflected in your horse; he is stiff through the neck, back, and mouth.
You're ankles are down in one picture, up in the others. It seems to be moving around quite a bit. Concentrate on keeping that lower leg still and resist the temptation to let your grip sneek into your knee. The flex stirrups that you are using give many riders alot of trouble. It tends to make you stiff in the ankles. Traditional heavy irons are best whan you are trying to keep you heels down and lower leg still.
In the first picture you are over posting and have pushed up off of your toe.
I think your biggest position flaw (and its not even that big
) is your extremely stiff upper body. Your arms, wrists and shoulder are all locked. Your back is also very flat but very stiff which means that your hips and seat are prone to stiffness too. This has cused a chain reaction throughout your entire body resulting in a tense horse.
Your arms and wrists must be soft and forgiving. Relax your shoulders. Roll them a couple times when you are riding. Keep those thumbs up for a straight contact to your horses mouth. Make your reins a little longer and let up off his mouth. As your reins are now he has no way to flex at the poll and bring his back up to you.
Remember, outside rein supportive, inside rein encourages flexion. If your inside rein is not soft he will lean on it and hang on your hands. He must learn to carry himself and you have to encourage him to do that by being soft and inviting with your hands and seat.
You two make a very nice pair!