Well since you just want a theory...
After reading Dr. Howard's article, i noticed that the structure of the penis is much like a building in reverse. That is to say, the structural members of the system are in tension versus compression. These structures, along with the outer tunica, limit the expansion capability of the penis in a sense that they reach their limits of tension and hold. In order for these tension rods to be extended, they need to have a larger tension force on them. For this to be done, it has to come from a higher pressure inside the penis.
Given a large enough exterior shell(tunica), the interior of the penis must have a greater amount of pressure applied to it in order to expand these structures. This is the reason that a higher erection quality is needed to increase girth. The higher the erection quality, the more probable it is to expand the tension cables father than their current capabilities. They are, thus, part of the expansion limitation of the smooth muscle in the penis.
If over trained, these cables/pillars will have a natural muscle reaction to being hyper extended and limit their expansion in order not to be severed. This is why appropriate healing is needed and why in some cases a marked decrease in girth may be the precursor to an increase in girth. Once these cables "heal" in a sense that they achieve a muscle memory of a higher degree of expansion, they'll release their previous tension and allow the Cavernosa to expand further...
Is this true? hell if I know, but it sounded good coming out LOL! You said you wanted a theory, i just came up with one
