Mature Metal discussion

I’ve never used a chastity device before, but I’m currently measuring up to order a Queens Keep from MM. A couple of weeks ago I purchased the sizing rings and have been wearing one nearly all the time since then. Here is where things stand; the 2” ring sits very comfortably on me, yet there have been times when it slips off by itself. It seems my penis might retract into a turtle shape and slide out, or perhaps one testicle manages to slip inside. I tried wearing the next size smaller, 1 7/8”, but that left me feeling exposed and chafed at the base of my penis within about 24 hours. My questions are; will keeping the cage on help keep the base ring from slipping out? Should I look into getting a ring sized at 1 15/16”? Would an oval-shaped ring make any difference here? My partner and I want something comfortable enough for me to wear continuously until she decides it’s time for unlock. Thanks in Advance.