i just had all these problems with my pony, hes not strong at all, but due to his funny shape mouth, and leaning, i tried a waterford best thing i did for him... not sure its dressage legal though.i dont think it would be....have you tried the loose ring schooling bit, its a half moon bit, ?...
i have a 12,3hh welshie x hes of the moors. hes 16 yrs old... we just hack, done a few shows.... we live in cornwall.... as soon as i work out how to add pictures i will put some up.....