We are at this same point with Alax. He has a great strong trot, but it is much more elevated when he starts to lengthen his stride. You can see it in his shoulders from the box. My goal for this year is to really help him and me understand how to get an elevated, lengthened trot consistently. So far what I have found is that I need to "milk" the reins before asking for more impulsion. I suppose this is Leia's "collect and balance" she describes. If you have ever milked a cow by hand (it's a good analogy around here, as lots of people in Wisconsin have!), you usually pull one teat then the other (on that side, there are four teats total. Ya'll watched Little House on the Prairie, didn't you?). So if you "squeeze" one rein then the other, right, left, right, left, etc., that is what I use to set him up before and during asking for more impulsion.
As far as posture goes, Leia's description of what NOT to do sounds exactly like what I do in what I call Marathon Mode.
It's when I don't have to really help Alax set up too much, because he already has continued implusion from being "excited" in the obstacles, and I am "choked up" on the reins to help make harder turns. (The photos on my website where Alax is looking really good are from obstacle classes, not arena classes!
) What we need to work on is transferring that "ambition" to the arena, where he usually isn't quite so motivated. Yes, I need to think, too, about my motorboat, keeping that energy in the hind without losing forwardness.
I had a lot of problems last year with him popping a shoulder every time I asked for more impulsion in the arena, so then I would have to "reduce" his trot so he didn't canter. Ultimately, he would speed up some, but not extend or lengthen because of the popping.
We have seen some moments of brilliance this winter. I have a lesson in June with Muffy Seaton, and I am hoping that she can help us with this. That, and raising the base of his neck.
Myrna