Dennis Hooker wrote:
If you have trouble making any kind of yonkyo work try this. Use your left hand to apply sankyo so you partners right hand. Tighten up all the tendons am muscles in his forearm with sankyo then apply yonkyo with your right hand. It is not the traditional way I was taught but it gets to the meat of the technique and not the membrane around the bone. To do the other side turn, blend, mix and repeat.
The way we do usually yonkyo at our dojo, it's close to the way you describe it and, other times, it's close to sumiotoshi (if we do it from, say, katatedori without going into ikkyo first). Either way, though, it's seemed very much to me that it's about kuzushi less so than going for pain.
I once asked my teacher once what the difference was between the sumiotoshi-like version of yonkyo that he does and sumiotoshi. He thought for a moment and said that, in principle, there really wasn't much difference. But, he pointed out (like Dennis above) that if you control the wrist joint (between the forearm and hand), uke's entire arm will get affected (ie locked up) moreso than if you don't.
This whole thing reminded me of some folks I know who use the bottom hand in a "traditional" yonkyo to apply a nikyo lock to the hand/wrist. (Easy to get into from a regular nikyo if someone tries to stand up -- keep the nikyo and shift the "inside" arm into the yonkyo position.)
PS: Mark, I, for one, would be interested in reading "Part Two" of your yonkyo thoughts...