Sounds like the silicone ring is not seated firmly behind the glans so that the excess skin is able to crawl back out after being tucked into the sleeve. We can make a tapered sleeve or a standard straight sleeve with a smaller silicone ring if required for a secure fit.
You can try holding the underside of the silicone ring beneath the glans and use the other hand to pull the skin at the base of the shaft near the ballsack opening to draw the skin all the way down the sleeve. This will help prevent it from working its way back out when tucked in behind the ring. Check to see if the ring is seated directly behind the glans. If you are still experiencing slippage then you definely need to make some adjustments on the sizing for a better fit.