Interesting Dan, and thanks for the very useful thread btw. I was noticing just in the last year or so that instead of it feeling like I was able to run pressure into the ground through the bones (say when resisting in pushout) it started to feel more like I was wrapping the incoming pressure around myself through the skin and then it kind of just went around me. Kind of like when the input coming in my right side collided with the input coming in my left side they just nulled each other out across my back. Hard to explain, but I've been told it does feel different to those folks pushing.
The stretchy feel can be things connecting and that is good. What and how things are connecting may not all be the same. I don't know how you train but after watching you move I have an idea. I don't usually deal with left side/ right side, instead I train the left hand to be controlled (through the center) into the right foot and vice versa. The joining that you are "sensing" is and can be just
felt across the back if that is all you're training. But their are connections deep in the front as well. There is a limit to just training, pulling, using the back line that can lead to problems / potential weaknesses etc. If you consider central equilibrium (what I used to call "zero balance point") the back must be supported by training opposites. Some people do up/down, side/side, and front/ back one way, and some do it differently. It isn't all the same.
One can lead to back problems, flat feet, overly stretched and tucked sacrum and double weighted hips. Other ways lead to very flexible hips that are very difficult to throw and with a power absorbtion/ generation that is markedly different from the previous approach, IME it is also just about the only way to do Koryu weapons -truly effectively- while leaving the feet and weight free.
I tend to demonstrate going from long weapons in rational use (not as a training tool) to sword, to twin sticks to empty hand, and how the body method is rational and consistent throughout.
I have not seen many methods that have a cogent rational throughout that makes consistent sense with the types of men I usually converse with. Many times they are art specific, spotty and will not translate well.