When you’re riding & your horse is moving through from behind and on the bit, it should feel as if you’re holding a pound of butter in each hand. Light in your hands, but still connected with your horse. When the horse comes behind the bit, you lose them in your hands because they’ve tucked their nose behind the vertical and you lose your connection & it feel like nothing is there. Even when your horse is light and moving through from behind you should always feel them in your hands. Going behind the vertical, is usual seen with green horses or used as an evasion. It should be fairly easy to correct ( I have this issue with my own horse at times). Use your leg to move your horse forward in the hind end. With my boy a squeeze & cluck is enough to get his attention back & moving forward, he comes back into my hands within a couple steps. It should be a small correction. Hope this helps!
keep leg on, you should always be using twice as much leg as hand. that makes then work from their back end and push with it
If you were to draw a straight line from the horses pole to the ground, their nose should be at or a little before. If it is overbent they are behind that line
Typically the 3rd vertebrae should be the highest point of the horse's neck if they're on the bit. Anymore than that and they're over bent. But "on the bit" is more than just the head position, it's when the horse is working all through their back and hind quarters which causes the head to come down and work.
bungies are great as well it allows the horse to drop its head out long and raise there back
I use draw reins they seem to help my horse to flex properly