I have the same problem with feeling leads on my horse. I have to really work at it to tell which one he’s on, even if we’re making a turn and he’s on the wrong lead. He just…most of the time, manages to do it so well-balanced that it doesn’t feel ‘wrong’!
Uh, anyway. It could be a fitness thing like mentioned above. Does he tend to use the same lead all the time no matter which way he’s going or does it get switched up? Does he do it on the longe line?
For a schooling show though, I agree with wyoenglishrider…just use simple changes and don’t stress too much about landing on the correct lead because otherwise it sounds like you’re doing everything at home you possibly can to help him figure it out. Heck, maybe putting him in a new environment will help.