Phi, that's an excellent example and damn if Ushiro isn't hitting the three fundamental pieces . . (my interpretation - someone else feel free to jump in and disagree):
1) Connected - Make the physical connection between yourself and the other person (this is easy, it's accomplished on touch)
2) Unity - Unify your center with the other person's so that you are a "four-legged animal" that you are in control of (this needs to be felt and grasped as a "skill", then conditioned with training partners giving you a dumb force to work with so that you can develop the skill)
3) Change my inside - Move your center through the other person's center and you will move them (the internal part of this being that once you have some skill, you don't have to visibly "move" to accomplish this based on what most observers can see, hence uke's balance moving back until it's broken while Ushiro doesn't appear to "move"). On a related note, I've heard from attendees to Chen Bing's lessons that his recommendation on addressing an incoming force (push, pull, grab, etc.) is to "change the inside".
Anyways, them's my $0.02 based on Phi's example - anyone want to add, disagree, or otherwise participate?
how's about using an example as a way to start the discussion?
uke stands in forward stand with fist out like so (hopefully the image shown)
nage stands in natural stand in front of uke with left palm rested against the front knuckles of the fist (i had seen Ikeda sensei did it with one finger and on the receiving end of such finger too). so, Ikeda sensei was nage. he would said three things (with accent): "connected", "unity", "change my inside". after a time, slowly, you can see uke posture shifted slowly toward his rear "third leg" (toward right rear) and lose his/her/it balance and staggered. and you will notice that Ikeda sensei body didn't move.
so, would that example be an ok starting point for the discussion?