In my opinion, the bit fits perfectly fine in his mouth. You cannot see any of the actual bit bar outside of his mouth, only the snaffle ring, which is what you want. It’s when the bit bar sticks out of the mouth that you know the bit is too big.
But the cheek pieces on the bridle sit out too far from his face. They should be against the sides of the face, not have a gap. Plus the pony has no “wrinkles” in the corners of his mouth, that I can tell on the pictures.
I think you need a smaller bridle, not a smaller bit. Or at least punch holes in the bridle to make it smaller.
With my 36" mini, I got the smallest bridle I could find, and it was still too big, so I punched extra holes. I’ve got a big “tail” of strap that flails away from the keeper near the buckles on the cheek pieces, but at least the bridle does fit her, and she has wrinkles.
From the little I’ve learned about cavessons on driving bridles, you do want one to be a totally separate piece from the bridle if you’re using a snaffle. So definitely add a cavesson if you want one. I bought a harness for a mini that didn’t have a cavesson, and I prefer to use one, so I bought this for it:
http://www.ebay.com/itm/Miniature-Mini-Horse-Driving-or-Riding-Biothane-Caveson-/140354897856?pt=LH_DefaultDomain_0&hash=item20adcdc7c0
It was perfect for my needs.
As I understand it, with the mechanics of cavessons with a snaffle bit - a separate cavesson will simply act to assist in keeping the mouth closed (and aesthetically give the appearance of a “finished” bridle). The English/Dressage person in me can’t live without one purely based on looks.
Some driving bridles have a the noseband actually built on to the whole bridle, not as an adjustable piece. I think if I remember correctly this was not considered good with a snaffle because since the noseband is literally connected to the same piece you attach the bit to, when you use the reins, the nose band is additional pressure onto the bit everytime you pull the reins.
However, then I was also told that for a leverage bit, or something like a glory bit, you would want the noseband actually attached directly to the driving bridle, because it helps (slightly) keep the bit stay in proper parallel to the horse’s mouth when you use the reins, and assists in providing proper leverage (almost like using a bit keeper on a full cheek riding bit, as I understand it).
I think I said that right? Maybe someone can correct me. I learned this a little over a year ago. I just remember the clinician saying that for a snaffle, you do want a separate cavesson.
That being said, 3 of my 4 harnesses all have separate cavessons. The 4th one, for my horse, has an attached noseband that is part of the bridle, and I use a French Link Snaffle with him, and certainly have never noticed any type of problem that could be associated with unwanted pressure on the bit.