didn't you post this issue on another thread? I might be confusing you with someone else.
The thing is to get him going forward really committedly first before asking him to come forward AND onto the bit. So, ride him out and ask him to trot or canter and really get him moving, but don't try to hold him with the bit or seek for any sort of headset. Just go forward off the leg, no holding back.
A horse that learns to come behind the leg or the bit is very hard to train out of this, so work to get him mentall focussed on a good , working forward.
The appy I ride is kind of like this. If I post the trot, he thinks I want to canter, so it's hard for me to get him to trot out the way a dressage horse is asked to canter. His ownder can do it, but she has to wear spurs and cna't take up much contact at first. He will even do the trot in front canter behind or is it the other way aorund?
I just don't ride him in dressage. So basickally, I gave up and I take him for the western horse he is trained to be. If he half canter/trots, I will push him forward in a brisk canter. He prefers to canter anyway.
Good luck on your new project. Think forward! Then work on "on the bit"