Mo,
I got that pic off the link you posted. If you look very closely, those “ribs” or “dividers” definitely look like they’re part of the tunica - unless the illustrator made a mistake.
Admittedly, I don’t have exhaustive knowledge of penile anatomy, so I’m not going to argue trabeculae/tunica/sinusoids, etc. But I have good vision and I see what that illustration depicts.
Also, I disagree with your statement: “The idea is that jelqing works by applying pressure to the CCs from within. The resulting pressure would impact the longitudinal and transverse surfaces within the CCs equally (pressure applies the same force per unit area in all directions).”
Consider the mechanics of the jelq:
(1) The pressure is being applied externally, not internally; hence, where and how you happen to be gripping has a direct affect on the pattern and focus of the pressure relative to the length of your penis.
(2) During the jelq, the hand moves forward; only the penis directly under, and forward of, your grip is under pressure. In other words, this pocket of pressure is moving forward - it’s not stationary.
After a particularly intense jelq session, I get petichiae the worst at the tip of my glans - which can actually be aching. I think that suggests that pressure is moving forward, and not “equally….in all directions.” If this is true, then the moving pressure is affecting those chambers in one direction.
But in bi-directional jelqing, force is moving towards the glans and also towards the pubis; this cannot be the same as regular jelqing.
And while clamped, or especially while doing horse440s, the pressure is much more uniform, as you’ve mentioned. It’s also persistent.