Don’t know if this would be any help to you or not.
If I understand you correctly, you need to fit the barrier ring around your stoma but the hole in the ring is not big enough to fit around it? Correct?
I do not use a convex anything, but this is how I was taught by the nurses at the Mayo Clinic following my 1st surgery:
1. Cut flange hole to fit stoma (obviously).
2. Cut the barrier ring into 3rds.
*My stoma has changed size many times through the course of my 4 surgeries so I currently cut it in half.
3. Roll the portion of the ring that will be used into a ball (save the other portion(s) for the next change). The warmth of the friction makes it pliable – I usually use a hairdryer to help warm it.
4. Roll the ball into a spaghetti-like “worm” trying to approximate the circumference of the flange hole you just cut.
5. Lay the “worm” along the perimeter of the flange hole, trying to keep it slightly to the outside of the hole’s edge. You do not want to see the putty ring peeking through the hole when viewing from the bag-mounting side of the flange.
6. Press the flange/barrier ring combo onto your body and then remove the paper backing strips from the adhesive part of the “Band-Aid” portion to the flange. (I am kind of anal - pun intended - about getting a good seal so after placing the flange/barrier ring combo, but prior to attaching the bag, I use a Q-tip to burnish down the area where the barrier ring is.
7. Attach bag and warm the area (I use my hand) for a minute or so.
I know you stated that size is an issue so, if needed, I assume you could “roll” as many full size (uncut) barrier rings together as you would need. The stuff is like Play Dough.
This is the only technique I have used in the 7+ years I have had a Barbie butt and I have only had 1 leak, and that was because I got too aggressive using water to flush my bag.
Hope you can use this info!
***Sorry for the formatting of this post. I have tried everything to try to get it formatted correctly. I hope it isn't too confusing.