You are such a darn good rider, you better stop nitpicking yourself! You ride really well, so these improvements are like icing on the cake, ok?
That said, if you want my two cents, you got it!
Picture #2, where you say he was tossing his head, If my fav. You are aligned picture perfect top to bottom, not looking down like in many other shots, there is a perfect straight line from elbow to bit. It’s hard to see, but it looks like you are curling your wrist over a bit, and while that’s technically a no-no, I find it a simple way to get a bit more connection to the bit, when the horse is needing a reminder to not lean on it. First would come just a “milking” of the rein with the fingers, then a bit of the wrist tightening and rolling, then a firming of the elbow against the side of your body. I think when you are thinking about lifting him off the bit, you get a bit more engagement, which would be amplified if you could get more forward from behind. A crop?
On the larger horse I can see that he is harder in the mouth and you have a harder time being connected to his mouth, and you then end up with a slowly straightening elbow, as evidenced by the last photo. In that canter shot; your position body-wise is elegant. If you dropped the rein entirely, looked up and not so far into your circle it would be picture perfect. Would that horse be a good choice for lunge line lessons?
All in all just two things to keep in mind; Elbow connected to ribs and head up , not overturned to inside of circle.