Cinny, have you ever tried eggbutt on him? For whatever reason my qh hated the loose rings couple times I tried them (exactly same mouthpiece BTW) and tossed her head. If you could borrow one from someone in barn, I'd give it a try.
Ha ha, we tried an eggbutt for about a week and a half, he HATED IT. These are the bits I have used.
1) plain old loose ring sweetiron snaffle, when I first bought him and it was only used for getting him used to having a bit in his mouth and lunging, I never rode him in it because I was doing his first rides with a side pull.
2) Plain full cheek snaffle, I used this to have a little more turning power as he was learning. He learned to brace on it so I went to....
3) Fulmer. I used this for about 6 months and he did okay in it, but I think it had too much nutcracker action for his liking. My seriouis Dressage trainer had me go to
4) Sprenger WH. He did fine in this, didn't seem to care for the roller and developed a reaction to the Aurigan, who knew???
5) Change to the copper snaffle in the link above. He really seemed to do well in it. Changed stables and trainers, new trainer had me do
6) Similar snaffle in an eggbutt. Head tossing and gritting was worse plus he would add in a side to side action similar to horses who "weave" in their stall, only he would do it while riding. He also started experimenting with bracing against it again,something he can't do with the loose ring.So I went back to
5) Copper snaffle and we have stayed here.
He is always accepting of this bit and we never have any bridling issues at all, sometimes he actually grabs it from me like it's a treat. I do occasionally have issues getting to "drop" the bit after riding when I go to take the bridle off and will try to grab it back. I've never had a horse do this before.
He seems to like it, it's show legal, he works decently in it and I'm hoping he will work even better after his dental, so we will probably quit with this one :)