What I pick up from the horses, both geldings and mares, is that just having the curb in the mouth reduces confusion. My hands can feel the horse’s tongue “consulting” both bits (one at a time), then they obey my rather light and well timed hand aids on the bradoon. It is sort of like the horses “want” a “second opinion” about what my hand aid means for sure.
In a thirty minute ride I might tweak my sagging curb rein once or twice during a ride (immediate release), never fully engaging the curb in that the curb chain does not tighten against the curb groove, or if by my clumsiness the curb chain does tighten against the curb groove my immediate release removes any pressure the curb groove may get. Basically all I am doing with the tweak is saying “yes, I did give you an aid, this aid is not an accidental aid,
and it would make me happy if you obey this rein aid to slow down.”
I have come to a tentative conclusion. Using a snaffle for all hand aids–slowing down, turning, collecting or extending, means that the horse has to use a split second to decide, from my seat and legs, exactly what I am asking for. With the double bridle I can use the bradoon for contact, turning, and a slowing down aid and the horse seems to act like my hands aids are much clearer to them and the horses seem more confident that they are obeying my hand aids correctly. Currently I only use the curb to indicate to the horse that it might be really nice if he moved some of his weight off his forehand for a while, previously I did use the curb as an emergency brake (briefly) at a full gallop but since I am no longer galloping around in the field or on the trail I no longer use the curb as an emergency brake.
If the horses indicated in any manner, shape or form that they did no like my rather odd double bridle set up I would change the bridle before my next ride, in consultation with my riding teacher of course.
I check with these ladies regularly about whether the horse shows any anxiety about the double bridle or how I use the reins, and they both tell me that the horses look happy, happier than they do when I rode them in just a snaffle bridle. Neither lady wants me to change back to just using a snaffle on my Micklem bridle. They both have also told me that I am the only rider at their stable that they would let use a double bridle, odd but true considering how badly my MS has crippled me.
The Micklem bridle avoids the facial nerves which means the horses are much less irritated by the bridle. The double bridle bits (titanium) bring them clarity while also giving the horse something to “play with” in their mouth. Because the bradoon hanger goes over the crownpiece the Micklem crownpiece can work as designed and if I do use the curb bit stronger the padding on the Micklem crownpiece helps to ameliorate any extra pressure I might put on their poll if I fully engage the curb bit. Because of my odd reins (odd for a double bridle) I can make sure that my hands are even on the reins which reduces confusing rein aids, and my riding teacher has an easier time telling if one of my hands if off by an inch or two from its ideal position on the reins (and believe me, she will tell me to fix my hands!)
My riding teacher and I fully discussed everything about my odd set-up before I put it on a horse. She is happy with me, the horses seem to be more cheerful with my rein aids than they are with a snaffle bridle, and I am happy because both my riding teacher and the horse are happier with me.