I'm hardly an expert, and I might be missing your point, but my understanding is that openings are found, not made. We can lead aite into providing an opening, but it's much like the proverbial horse and water. The premise behind adopting stances, i think, has to do with this idea.
I would also say that when you test your sensei by resisting the initial movement and the sensei then adapts, he's not creating the opening, he's finding a new opening through which to move you into the shape he was originally looking for so he can continue with the rest of the movement he's trying to teach (assuming he doesn't just do something completely different). As far as i can tell, once you have exploited an opening, you can then more or less move uke how you want because their structure is compromised.
As it relates to doing any particular technique, I think it's critical to realize that uke's structure should already be compromised. At first contact it should have begun to erode.
A well expressed post,Matt.
At a certain point I went from finding and exploiting openings to creating them also.So I understand Sifu Joe's verbage above.This connects to aspects of Takemusu Aiki, in my lexicon. It springs from experiencing openings in the manner that you described above and then they are taken to another level. How you get there is a matter of personal training.
As an uke, I am distinctly interested in connecting integrously so I might be as fully engaged as possible while also being available to learn from the (creative forces of the) techniques themselves. which constitutes the greatest kind of "receiving" I have,well, received.
Still, there is a lot to be explored; luckily.
As for testing sensei with resistance, I expect to be shown an opening somewhere a little south of my tail bone if I am arrogant or tactless in my choice of when to 'test' sensei. In other words, when my spirit/mind is incorrect it gets crumbled. But mostly, I find, i don't hear the lesson being given when i'm roughing it up when i ought to be listening.Not that anyone else would do such a thing. That is my own experience. Buyer be aware.