Thanks so much everyone for the info. Luckily I own several different saddles, so I think I will try different ones on my Foxtrotter until I find the one she goes best in.
I have one more question. If gaited horses don't really collect, how do I know if I have her in the right frame and not ventroflexed? For instance, my Mustang will tuck his head in and really get nice and rounded up and his trot will get smoother. I call that collection, at least for my level of riding ability. (I'm just a trail rider).
So how do I know if I have my mare going okay? If I can find the intermediate gait and hold it there for a little bit, do I know if I have found the correct position for both of us?