beperken

By using the double-affix notation, it is clear one is not deriving beperken from perken, but from perk. For the two circumfixes, ge- -te and aller- -st, the semantics are not very obviously additive. But for the three verb-forming circufixes, ver- -en, be- -en, and ont- -en, the semantics are additive, even if the additions are only possible in a particular order. This is similar to Latin ēlīminō, which is analysed as a double-affix, not a circumfix. It ought not be necessary to require this to be a circumfix if **līminō existed, despite that ex- is only added to verbs.

I'm half-convinced by a slightly different argument: that this is the circumfix to form transitive verbs from nouns. I appreciate your explanation, though, even though the power of the construct for the application surprises me.