If horses tend to toss the head it makes sense to attach a second rein to the lower cheek piece ring to apply pressure on the horse’s poll. The horse will try to dodge this pressure by lowering the head. The curb chain should come into play at maximum angle of 45° (lower cheek to horse’s mouth) to avoid the horse lowering its head too much.
It is very common to use a double rein as it enables the ability to apply pressure on the horse’s poll if necessary. Pelhams are also widely used with Pelham straps. This strap is attached to the upper and lower cheek piece ring and the rein is fixed to this strap.