If the tunica only has 5% elasticity in it's tissues, then wouldn't gains made from tunica stretching be really permanent since it'll be less likely to "snap back" to the length it was before?
As for the 5% elasticity thing, are you sure that's true? The penis seems pretty damn flexible to me. I mean, just being able to go from it's flaccid size to it's erect size sure seems to prove that it's a very elastic organ.