Two columns

Today I was doing what I am calling the modified planking. Just leaning forward against something in a seated position. When I do this I feel like I am able to better feel a stretch on my back that I cannot feel standing vertically nor do I feel like I have the ability to sense these stretches doing the normal planking. So I was doing this modified planking for a while and working on feeling this back stretch and then when I did the normal standing the part on my back that I normally associated with the back of the U which normally just feels like a thin sheet which stretches from the back of the top of the diaphragm downwards now felt like two separate columns on the back.

I hade made a blog post in the past about a transverse stretch feeling and in response you drew a picture of two columns with screw like threads. Are these two columns supposed to be felt along the back or are they more in the center of the body. I also had always wondered/thought that my feeling of the stretch in the back was maybe something that was a part of the diaphragm or connected to the diaphragm but this time around when I could feel the two columns they felt distinct from the diaphgram. When I would breath I could feel breathing parts of my body, lungs, ribs, etc moving but the columns didn't seem to change in relation to the breath.

Inky sketch of shift and side thrusting routes