What do you think is happening in this situation that makes it difficult for Uke to get up from the pin? What makes turning the palm up or down have this effect?
I'm asking because I would like to know more about what you think the phenomenon causing this result is.
From what you just described, I would say you are describing something different then what I was getting from other people when I made an attempt at creating definition "D". To me, Definition "D" has a feeling that nage has trained his way to correctly make adjustments to the situation. But what you are describing, at least from what I read is related to something going on inside of Uke. This is why I said it seemed to me like "proper technique" and mechanical advantage. Maybe mechanical advantage wasn't far reaching enough, maybe I should have added "and/or inherent mechanical weaknesses in the body".
If I were going to make a quick definition of proper technique, maybe something like:
Proper technique: Taking advantage of inherent mechanical weaknesses in the body by means of a superior mechanical advantage.
This definition would allow for things that exploited either nage's superior mechanical advantage, or uke's inherent weaknesses (maybe what's going on with uke's palm in your description?).
Frankly, I don't know. This is exactly what I am trying to discover at the moment why in such positions uke has an inherent weakness. The palm up example has many applications seen in many techniques. The thing is it is not even technique but alignment/position of the body. If the body has inherent weakness by such positions then I would believe the opposite holds true that there are positions that the body would hold inherent strength. Sorry but I don't know what goes on in the body why it has such an inherent weakness.