Chastity and orgasm denial discussion

About two weeks back, I decided to buy the CB6000. We spent the last week trying to figure out how to get it fitted just right and have resolved everything except one issue. When he sleeps at night, his penis swells and deflates quite naturally—at least for now—even with plenty of lube applied. This causes his cock to gradually move up along the shaft section of the device, leading to skin bunching and pinching in the area under the spacer between that shaft part and the ring. I’m going to try a slightly smaller spacer today, but any advice would be much appreciated. I’ve also thought about using those tongue attachments available on the market, but since he fills out the device well as it is now, I worry they might just create more problems.