Have you considered putting him on Estrone for his stiffles? I’ve had good luck with it for some of my guys that are just a bit weak and loose in stiffles. They don’t need to be on it forever but it helps avoid having to blister them.
But it still takes longer to get their core stronger…and you just have to keep riding and training. My point is to keep working on things. If he is really good at home and then the issue more at the shows…it could just be tension from the competing. So going to more shows–best if quiet schooling shows–and working on the tension. First show back after 2 years…I’d expect them to be a bit wild/excited! Just don’t over focus on his high head even though that is the thing you see the most