Issues getting the right base ring size

Hi there. I currently own a cb6000 and am thinking about upgrading to a jailbird. I’ve done plenty of research on how to measure correctly, and mostly feel confident in my results, but one thing is still bothering me: with the cb6000, I’m forced to use the largest ring because during an erection my testicles turn purple if I try any other size, yet when flaccid, the middle size feels just right. I’m not sure which direction to take now. Any advice would be appreciated.

I replied to you in the other thread already. My husband wears whatever size feels comfortable while flaccid.