Just because kings are riding a short tail doesn't mean that they are going to eat. It is my belief that they do not feed just because the opportunity arises when they are riding a short tail. I have seen them go past bait fish that are within easy range an yet they weren't interested. Much the same way that reef kings will swim amongst their prey on a reef without showing interest in feeding. When there is more than one rider, it is far more easy to get a take, and the more riders, the better your chances. Single riders can be hard to get to eat sometimes. Sometimes when you hook up on a rider, some of the riders will decide to go with the hooked fish and if you trust your mate, you can end up with a double. Likewise, if you hook up from a short tail carrying riders, your mate can also hook up off the same ray. I have hooked up and landed a king, gone back to the ray and hooked up again.
On the fly or not interested.