I was thinking about half halts and downward transition riding two horses yesterday, school master Andy and split personality Paint.
The amount of halt and the amount of go are entirely dependent on the energy of the horse at that moment, and it totally varies not just between horses but for the same horse from day to day or just during the same ride as they warm up, or maybe get a bit tired, or realize they are headed down the trail for home.
That I think is why the instructions are so nebulous. Everyone has a different horse in mind when they explain.
Plus a half halt is not going to miraculously move your horse to a whole new level of training. It can be part of training of course.
But if your horse is sucked back behind your leg, or upside down, or heavy on the forehand, or rolled behind, or having a racey or a lazy day, then they aren’t going to suddenly be lifted and collected and etc with aa just a correct half halt. Plus it might be difficult to get aa useful half halt rather than just slowing the horse.
I also think some dressage riders especially lower level end up with way too busy aids, bumping or spurring every step, or jabbing on the reins every step.
You need a horse that will go forward and keep that pace from one leg aid, that is has impulsion, before you can start altering the expression of that impulsion.
We talk alot about self carriage. Maybe we also need the term "self impulsion.’