I think just like all collagenous tissue there is a certain amount of strain that comes from uncrimping and orienting the fibers (aka newbie gains). Then there is a modest amount that is achievable through actual brute force strain prior to the physiological toughening response, after which there will be a plateau that is insurmountable. Together these might equate to around 0.25 to 0.5”. What you are describing to me sounds exactly like the result of chronic edema resulting in tissue fibrosis which would make the CS bulge and feel hard. The CS is not supposed to be hard, and if you have reached the point where it is, you have produced irreparable damage to the tissues. In that sense you have just achieved more girth by recruiting your body to add layers of scar tissue to your shaft. Not very appealing to me personally, but I’m sure that many here would say it’s worth the tradeoff.
That’s now really how Angion method works though. It basically causes supranormal flow rates in the arteries to stimulate arteriogenesis. The stiffening of the CS seems to be due to very high flow rates, like high water pressure stiffening a hose. I’m sure your theory is correct regarding reasons for gain plateaus though. It’s the only one that really makes sense ATM.
That aside, I’m curious about FIR pumping applications. Maybe a similar approach at gradually increasing hg, applying heat, then removing heat and cooling down at a higher hg.