Here are a couple of thoughts, some of which you are already onto. Bear with listing. Get back to me if pithiness sacrificed clarity.
-- increase stoma size, which you already did. I still mention as for me this was huge difference. Now I use 34 FR with increased holes' size. (Will post my DIY method.)
--an Ostomy nurse provided me with 28 FR size. Doubt it could mess with the valve. It was too flexible for me.
--put catheter in freezer so less flex.
--in addition to Kim's great dance routine, try inserting when standing or lying down. I used to clamp off the end for extra caution.
--check this site's master list of K-pouch surgeons for one in your area. If none, I get it. Do you see a GI doc, or does your PCP understand your GI needs? If so, perhaps one could arrange a consult with a Columbia NYC doctor--with you on line. While obviously I can not speak for their willingess, I know they are all in for educating other doctors about K pouches.
--do you irrigate? If not, your pouch might not be properly emptying. thus it soon feels full.
--any change in diet? Keep us updated. Lots of collective experience in our k korner. Jan