i assume your doing the normal version of join up. heres my less invasive more persuasive version:
walk out into your pasture, approach your horse (in a straight line! no being sneaky here) when your horse lifts it's head from the grass and looks at you or gives any signs it's focusing it's entire attention on you, stop, stand still, forget about the horse but keep it in your peripherals.
"so what, when i go to catch my horse i'll just do this stop/start motion depending on where my horse is looking?"
the more you do this, the better. in fact, do this for a month. provided you've done it right, a month will be more than sufficient. (the better you get at timing the release/stop the less time it'll take)
after this month, walk towards your horse, he'll look at you from quite a distance if you've done it right in the past month, but dont stop. keep the same focus on your horse, walking straight towards him, but walking slowlier than usual.
eventually when your horse takes the movement of looking at you to the point where he actually moves towards you, then is the time to turn around and walk away, UNTILL your horse deviates from walking towards you or puts his head down to eat grass, then you go through the whole process again.
this works on 100% of horses.
the theory behind it is one that most training uses, negative reinforcment, but this acknowledges the human as a negative. because in the eyes of a sensitive prey animal (horse) the predator (human) is a negative.
as a negative they'll be constantly seeking ways of avoiding us, this teaches them that the best way to get out of being with a human (predator) is to walk towards the human, very reverse psychological.
a bit farfetched yes, but i've made lots of money doing this with horses that were hard, if not impossible, to catch.
the advantages are that it develops a mental understanding between you and your horse, and the horse no longer fears you as a predator but accepts you as a member of it's herd and it's leader.
i've experimentally done this on cattle, kangaroos and zebras, and 100% of the time within a few short weeks these wild animals were all over me & following me around entirely tack-less.
it's very much similar i believe to join up (having never tried join up i wouldn't accurately know), but as i said it's less invasive and more persuasive, doesn't require a round or small yard (i've done this entirely in the wilderness, where the animals could easily escape beyond my reach if they wish) and depending on just how sensitive your horse is, less traumatic. and was made by me