Chastity and orgasm denial discussion

About four weeks back, I picked up my first piece of equipment, the CB6000s. While browsing around online, I stumbled upon this forum. After digging a bit more, I have some questions about fitting. The main one is ring size. Right now, I’m using the middle-sized ring with the smallest spacer. I started out wearing the second-largest ring for several days before switching down to the medium ring for roughly a week. Now I’ve read that you should be able to slip a finger between your ring and scrotum. But where exactly does this happen? Above the penis, on the side of the device, or underneath it? On the bottom, I can get my finger in quite tightly against the underside, but up top, there’s enough room for my entire finger inside the tube. I’ve also tried switching to the second-smallest ring with either the smallest spacer or perhaps the second-smallest one. The fit feels snug. It’s tough to slide a finger under the bottom this way, and I can’t get it into the top opening either. With that combination, sometimes I make it through eight hours, but other days thirty minutes is all I last before stopping because of that burning feeling. So I suspect my middle ring might be too big. Does that sound right? I’ve seen people suggest using a larger ring with the smallest spacer. That would mean going back to my current setup (middle ring + small space) rather than trying the second-smallest ring with a bigger spacer. I’m feeling a bit confused about which combo works best.