CB Range discussion

I’m trying to figure out the proper fitting method despite the being available. Even with the smallest spacer, the locking pin feels a bit short and only barely reaches the cage section. It appears that either the shortest spacer is too long or the longest locking pin falls just short; it’s not by much though—I need an extra 3mm roughly to make sure there’s enough hole for a lock.

Does anyone have thoughts or experience on how to best fit this? Thanks.