Here are some comments by VS Littauer:
Sorry about the picture quality.
He distinguishes between the forward balance of a horse (meant for going fast, or jumping) and a central balance used in collected gaits. Balance is never static in a moving horse. A horse trying to cover ground efficiently will have a more forward balance, and a horse moving in a collected gait will, by definition, shift his balance toward the rear and be lighter on the front end. Neither is wrong, unless used for the wrong purpose - you don't use collected gaits to cover a lot of ground, but they are fun and comfortable and useful for certain functions.
A dressage seat - a "classical seat" - is meant for a central balanced horse moving with a collected gait. If you use the same seat with a forward moving horse, your center of gravity will be behind the horse's center of gravity. And that isn't all bad, because a horse putting on the brakes shifts his weight to the rear (if he is good) and being FORWARD of the horse's motion is a good way to do a face plant!
A forward seat is optimized for a forward balanced horse - one moving efficiently over the ground. If you want to remain in balance with your horse's balance, you need to be prepared to shift YOUR balance while the horse shifts his balance. In a tight turn around a pylon, the horse needs to be balanced to the rear, and you need to help him by doing it with him. If you need to haul butt to the far end of a field, then a forward seat will help.
Thus I disagree with TL's statement: "If the saddle is designed and balanced correctly to the horse, and the rider sits up correctly, they should never be behind the motion, whether it is collected or extended.
" If you maintain a straight vertical line from heel to hip to shoulder to ear, you cannot have your weight forward enough to have your center of gravity match a fast moving horse. And that is why I agree with Littauer that "position" isn't important when compared to "fluid balance and rhythm
" - and that should constantly change.
That is part of why I like forward hung stirrups. I can shift my balance forward just by leaning forward and carrying my weight more on my thighs. That puts me in balance with my horse, and gets my butt almost out of the saddle so the saddle can pivot and not interfere with the horse's back. But I can also move my shoulders back, tuck my heels under me, and shift my balance to the rear (usually just before the horse does, if I do it right) to set the horse up for a more collected turn.
Of course, I also like Australian and English saddles with 1" stirrup leathers, and a design that doesn't force you on the cantle...
If the saddle puts you in the "classical seat", then you will need to fight it to get balanced with a fast moving, forward balanced horse.
Or, if you are really good, you can compromise by moving your hips and lower back enough to free up his back, in which case he will probably forgive your aft balance and move pretty good even though your weight is behind his balance. And if you aren't really good, you can adopt a position like the old cowboys, carry some weight on your thighs, move at the waist, and also end up with a reasonably content horse - although still behind the horse's center of gravity.
BTW - while I admire dedicated dressage riders, I tend to agree with Littauer that most recreational riders trying to imitate good dressage riders do a lot of harm to their horse. Of course, he also argues that most recreational riders need a simplified method for a forward seat, because we also lack the strength, balance and feel needed to ride like a top level jumper! I think instructors who try to teach position based off of experienced competitive riders do both riders and horses a grave disservice!