I've got an Arab with a small face, and just tried a bridoon loose ring snaffle on him. I don't know why I didn't think of it sooner - the smaller rings are a much better fit.
So, is it okay to show in as a snaffle? I've checked the rulebook, and the only thing I could find was a minimum diameter (10mm) for the bit - nothing about the size of the rings. This one is a Herm Sprenger Dynamic RS, and it's 14mm, so well within the requirements.
Can anyone confirm? I'd hate to get a surprise at our first show next year!
But.... just because no one has mentioned it... you can get smaller-length bits with different ring sizes that are in the "snaffle" not "bradoon" size range. The advantage of the larger ring is that it can move more through the holes in the bit as you work the reins (and "play" the bit more) and it can also give you a wee bit more leverage than a bradoon. The bradoon might "look" nicer but the snaffle might be more functional for your ride. Just something to consider.