Hmm, I think I've tried about everything you list! My thoughts:
"Contact" is more than "accepting the bit." I'd never expect contact to develop with a long rein.
TEACHING contact is different from RIDING the schooled horse.
RE-schooling a horse can involve unusual solutions, depending on WHY your horse evades the contact.
I'll be watching this thread, because I too get confused at times, when a horse described as having "good contact" looks like he's heavy on the forehand; or like he's really pulling and tense.
A horse can have all kinds of contact, and still be heavy on the forehand. He can have no visible contact with the bit, but be totally off the forehand, too. (think of a highly schooled Charro, or bullfighting horse that is ridden in a spade bit. The reins can appear to be fairly loose, but due to the nature of the training and the way very small signals are transmitted through the weigted reins to the bit, the horse gives to the contact and goes back onto his hindquarters)
He can have contact with the bit and be heavy and tense, and pulling, too.
So, I think it's more a matter of the hrose having and giving to
The horse decides where to contact the bit and give to it. You might have long reins and the horse go out to meet
the bit. He likely would not do that unless trained to "follow" the bit, and even so, once he has met the bit, he might either flex to it, or he might lean on it. All that depends on how you present the feel to him, and in fact, whether he gives to it or not is always dependent on the feel you present to him.
It's not a set system of you always hold this rein this way and that rein that way. It's , first you find the horse's mouth, feel of it, follow it, then you ask it to follow you.
In fact, it's that way in all of riding. First you "get with the horse", and then you ask the horse to "get with you".
ETA rereading I realize this sounds vague. Sorry. Will think more and maybe write better next time.