Since my lesson, I've been doing a lot of sitting trot work without the stirrups to work on having a deeper/more balanced seat and also making sure I have the strength in my legs to keep them at the right angle and in the right position. I've gotten pretty good at doing this at the trot w/out stirrups, and can tell it helps in my riding because I can keep my leg on Blaze better (he likes to drop out of gaits or pop his head forward sometimes).
Unfortunately, when I go back to the posting trot it feels like that hard work is going out the window. I have a tough time posting and keeping my leg back and heel down, which means that I end up having to move it back when I feel him about try and slow down on me just to keep it in the proper position. It's my chair seat coming back to haunt me at the posting trot.
Any suggestions on how to fix this? Posting trot without stirrups? Other exercises?