Since this is a Western Pleasure specific sub-forum, I'm not sure my view would help, but in general, getting a horse to use the hind end well helps build self carriage. I think by that term you mean that the horse is not just going faster and faster if you put a leg on, and dropping hard on the forehand?
So, yeah, you may need to have some use of a bit to ask the horse to not speed up, or drop the head too low, and plow onto the forehand. Is your horse leaning on the bit? are you using a snaffle or curb bit?
Some things that help engage the hind end are upward transitions , like a good leap forward from walk to canter, backing up, especially backing up a slight hill, doing roll backs, lateral trot work.
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