First off, Thank you so much, lots to think about and to be honest i think you've pretty much got him down, everything you've said makes complete sense and i fully understand were looking at tiny body language/cues and its so difficult to put these in words.
I'll answer the ones below as best i can, also i'll add a few little vids, they are basic and not intended for public consumption, so excuse me and anything else you see
You could try a different perch. What's that bright pink/red perch in both your pictures? He seems comfortable on that. Maybe unscrew it and see if he will step up on that instead? It will look different to him unattached to his house, so go gently.
I have wrapped his t perch in pink vet wrap, to see if that helps, i've tried his wood perches from the top of his cage and same reaction.
More importantly, I'm also wondering if the problem could be a control issue since he is perfectly happy to target from long distances under his own steam. Having control is a primary reinforcer. I'll explain further after another quote:
yes i believe this to be the case, if he's on his travel cage and wants down, you can tell as he kind of hangs around the edge looking at the floor, he will instantly step onto the T perch, sometimes, i return him to his cage instantly, other's i have a little chat, others i keep him for a few minutes, everytime he's on it he gets treats and such, as soon as he steps on he gets a big treat and as soon as he steps into his cage another cashew. (his big treat)
Perhaps the amount of time he has to stay on the perch is too long? Of course I can't see his body language and you say he will bow his head for a tickle which sounds pretty relaxed. But remember this is a bird who has no choice but to stay on the perch because he can't/won't fly... so in effect, he doesn't have much control about what happens. This could be the aversive associated with the perch - not saying that it definitely is, but that it's a possibility.
This does sound a certain possibility, ive tired a few times to do the below, so ill go over, have a chat offer the perch with a treat one end of his travel cage, he normally walks to the other end, i wait a few seconds or so and move away, come back 10/15 minutes later to try again, ive done this for hours and still he didnt want to play.
I would start again with the training. It may help if you use a different perch. To begin with, keep training to the times where you know he is going to be successful like from the top of his travel cage. But instead of carrying him anywhere on it, ask him to step off again. So step on, treat, step off. Repeat a few times. (Repetition in short bursts throughout the day builds learning.) Get him really fluent at this. When he's fluent, try in other places too.
i also tried this, he stepped up first/second time, i left the perch in the same place gave him a treat and let him step down when he was ready, a few minutes later tried again, nope, so left him, tried again later, nope, eventually i had to kind of push the issue a little and offer the perch mid way as he couldn't back off any more and he then stepped up, this was maybe after an hour or so and i needed to get him back to his cage.
little vid of him on it, maybe you can see some body language i'm missing, i have more on my laptop i will post later.