I appreciate your explanation of the horse and your being more involved in keeping him on a circle and such. He sounds like a really nice lesson horse, and you are lucky.
I think I mentioned in my original post the by having more contact and shorter reins you would better be able to follow his mouth and thus keep the contact constant. That's what is really important; solid and constant contact . As you get better, within that steady contact you will have variations of more or less resistance on the rein, but you won't go to loose unless you are taking a relax break after he is particularly good about something.
When I took dressage lessons my instructor made me work for weeks at a walk just following the hrose's mouth. I started out following passively, like almost literally letting him go where he wanted and my job was to just keep my contact to his mouth always the same.
Then we moved on to getting him to go in a circle and have a bit of flexion of the jaw towrad the inside 0 (not worrying about a total bend so no real leg on yet) and me following. Then we went to bend to inside and me asking the horse to stretch forward (follow him down) and pick him back up (follow him up) all NEVER letting the rein loop and never getting overly tight and never losing the flexion of the jaw to the inside. ALL at walk. I never got to trot for weeks until I could keep good steady contact, keep a small bend to inside and stretch and contract my horse longitudinally .
Then we worked on all that at the trot which is a zillion times harder.
Your seat is pretty steady now and once you get the feel for following the mouth AND getting steady flexion, (do this at WALK) you will probably find it pretty easy to transfer to trot and I bet your horse will get over his anxiety about contact when he sees that your hand is steady and trustworthy.
you've been a peach about accepting advice.