Hmm, Keith I think you've something there. When I do these dynamically, there's very little pain. As you said, I'm aiming to blend and take their center.
FWIW sometimes I tell students to think about sankyo like gently turning a chain. The first bit of turn contacts the second link. Once that is turned a bit it connects to the third. And so on. Eventually you have a moderately solid thing even though it is still a chain -- you've locked everything together. If you only have the first link or two you have to rely on pain since you have no connection to the rest of the chain. Done correctly you've started to "lock up" things starting at the wrist but your goal is to connect via that "chain" all the way to the person's center. That's not done with a hard twist but with a gentle connection. Once you have them all then you have a solid, connected "handle" of sorts rather than a loose, flopping chain. With the former you can control their center and move them. With the latter your only means of control is that first link relying on pain.