It is the right spacing between the bottom of the cage and the bottom of the base ring that grips the scrotum and holds the device in place firmly. It's almost counterintuitive, but by going to a larger cage you can actually get a better fitting device because you decrease this spacing. If you can't go smaller on the base ring, your only options are to close the gap or get a larger cage. Don't feel too bad if you don't get it right the first time. I bought my first MM device only to have to sell it and buy another for a better fit. Even with meticulous measurements, it's really a crapshoot to get it right sometimes. Don't give up. In the end, it is worth it.
Current Device: Unlocked but still Orgasm Denial
Previous devices: CB 6000s, CB 6000, MM Queen's Keep