Back in 1998 I had a situation in which a "septum" or wall of tissue developed in my pouch. As a result stool was not emptying properly. What it felt like was that something inside was blocking stool from emptying out of the pouch. Testing (pouchoscopy) proved that this was in fact the case.
I had 2 surgical J Pouch revisions to correct the situation, one in 1998, and then a second one in 2000 when the "septum" returned. My surgeon at that time compared the J Pouch to the British car Jaguar. He said it's a nice car, but it is high maintenance, and sometimes needs to spend some time in the shop for repairs. But he added that he was like a very good Jaguar mechanic and he would tune it up.
I never had any structural issues since the 2nd J Pouch revision in 2000.
I think you may have a similar problem to what I had. It is fixable, but the problem I had was not explained as a widening of the pouch but rather a compartmentalizing of the pouch due to the septum, which was cut and stitched.