It does NOT fit him .. When you sit in that it will sit straight down on his back there and will be pretty un-comfortable for him , not to mention it could cause him some damage
You would have to use a lot of padding lift the saddle to get enough clearance because the pad winds up compressed. As you get more lift in the front, the remainder of the saddle will also be lifted and will float on the horse's back. This usually results in the rider tightening the cinch even more which compresses the pad and then you wind up where you started. If you ride with the saddle rubbing the withers a condition called fistula could develop. This is an infection of the bone and is extremely difficult to get to heal.