Why Are Circles Still Eluding Me?

Arrrgghh. It's the bane of my riding existence. I can't ignore it any longer. Well, more precisely, Sue my teacher won't let me ignore it any longer and I guess I should (and do) thank her for it. I straighten the quarter of the circle where I leave the tangent point on the open side of the circle and head for the tangent point by the wall. I've done this from the time I started doing circles with Rogo. He'll do it at that point no matter where I start. I thought it was better, or even fixed at times, but today proved it wasn't as Sue worked with us on it. I didn't even know I was still doing it. Because I have him flexed / bent in, I think he's on a circle, but all he does is bend his neck and go in a straight line for that portion. Not being able to see or feel it anymore makes it even harder to fix. Sue tells me what to do - outside leg and rein to keep him from going out straight, but subconsciously I put my inside leg on anyway, to bend him, and then drive him out. It's driving me nuts!
Okay, enough of that. I just have to keep working on it now that I'm aware that it's still a problem. It's more upsetting to me than so called 'bigger' mistakes and challenges though, because it's such a basic and it shouldn't be an issue at this point and because I can't see and feel the problem and the fix.
Other things are going well. The canter steering is greatly improved, but keep in mind we went through a period where it was non-existent two or three weeks ago :) He wasn't happy about using his hind quarters, but he's much more relaxed about that now.
I'm really happy with the trot work. Can you believe that I can't remember the last time Sue told me to push him forward more? It used to be every few strides. Now it's been two or three weeks since I heard it. That alone is like a miracle to me. She actually tells me to steady him (slow him) once or twice a lesson. Rogo has become quite happy with his new forward. Sue told me to look in the mirror a few days ago as we were trotting serpentines wall to wall because she wanted me to see how he was happily swinging his tail from side to side. I saw a happy, relaxed, forward horse, using his hind quarters and swinging his back. Yippee!!! He's like this all the time in the walk and trot now. The canter is improving too, but the circles need work of course.
Yesterday we did 10 meter trot circles, three times down each long side and went around the ring like that. We did them for quite a while each way so we could develop a good feel for it. This was a new exercise for us. When I really focused on relaxing and using my seat and legs we could do them with very little rein aid. When I did use the reins it was mostly the outside rein, so I'm getting the feel for steering this way. It's a big change for me. I've always used the outside rein as a strong support, but the way we're schooling now it is the main steering rein with the inside staying quiet and used only as needed. So to do the circle you feel (or more if needed) the outside  rein in time with the stride or as required to keep the circle. My rib cage is a bit sore today from turning my body in alignment with the turn. I wonder if Rogo feels the same?
Here are some other exercises we've been working on:

1. trot three loop serpentines wall to wall and walk across the center line
2. walk and halt and remain immobile long enough to reinforce no movement. Do this repeatedly going large. We needed this because Rogo liked to wiggle and fidget when he halted but he's mostly over it now.
3. walk canter walk - only one day, but it went well
4. facing him into the wall and 'leg yeilding' up the wall (except that his face stays directly facing the wall, not angled)
5. trotting loops - corner letter to center line and back to corner letter
6. sitting trot - it's coming but needs work. I hold the bucking strap lightly at times to learn the feeling for keeping my hands more still when I sit.
7. canter 20 meter circles, down long side, repeat. Cross diagonal and trot at X.
8. For my equitation we've been focusing on stretching my core up with shoulders back, and keeping my knees from gripping.

I'm enjoying the experience of being at the barn sooo much. The people there are amazing. I couldn't ask for a more positive and energizing environment to learn in. I think I'll do a post on some of the horses and riders one of these days.