It’s very hard to find good information about this stuff online. My belief that the ligs don’t really matter is based largely on the fact that I can stretch my penis at 10 o’clock or so and feel the stress extend all the way back to my pelvic bones, where the crura insert into the ischiopubic rami. If, instead, I felt pulling against my pubic bone, I would conclude that stretching the ligs would help. But that’s not what I feel.
Certainly, I do feel pulling on my pubic bone at lower angles, but those aren’t the angles I normally use for sex, so they’re not as interesting to me. I sometimes feel some pulling toward the sides, and I wonder whether I’ve got some lig fibers attaching in weird places—off center of my pubic bone.
I think the dense cord of connective tissue you feel is actually the dorsal thickening of your tunica. This link might help describe that. Its fibers run from the glans all the way to the pelvic bones (ischiopubic rami). However, some fibers of the tunica’s dorsal thickening extend up and merge with the susp. ligament.
If downward stretching helps to lengthen the dorsal thickening, then I’m all for it. And I suspect that many of the principles that apply to lig stretching will apply to stretching that structure. So, you certainly haven’t been wasting your time thinking about lig stretching. Both the ligs and the tunica are collagenous tissues. What works for one will probably work for the other (although the numbers may be WAY different—the tunica’s one tough mother).
One other titillating fact is that the tunica splits into two sections as the CCs separate inside the body. Each "leg" passes through a muscle (ischiocavernosus muscle) before inserting, tendon-like, into the ischiopubic rami (the bones you sit on). I sometimes wonder whether penile growth inside the body (inner penis, if you like) is the result of stretching these muscles and tendon-like insertion structures.
If this is the case, then some gains can be achieved by alternatively stretching at high angles, to stress these deep connections, and then at lower angles, to stress the connections to the pubic bone. The combination would allow the internal structures to be stretched enough so that new length could appear on the outside. You wouldn’t be pulling the inner penis out. You’d rather be stretching it, so that any resulting growth would be seen outside the body (since the internal attachment points are fixed, any growth has to push the glans forward).
This see-saw technique has been discussed before, by Hobby mostly. I don’t know what luck he had with it.
If it’s possible to summarize this rambling, I’d say that principles of lig stretching certainly may apply to penile growth. It’s either the tunica that responds to the stress or the attachment points. But the results are the same—the penis extends farther out.
If it’s only the attachment points that stretch, this would suggest an upper limit on growth. You can only stress these connections so far before the whole apparatus becomes fragile. If the tunica also grows (and I think it does), then it’s harder to see a necessary upper limit.
Note that, for me, this discussion is mostly academic, since I’ve never gained a smidgen through hanging, despite having labored like a soldier. My gains came from jelqing and stretching.