This rule seems odd, but is clearly attested in ᴹ✶kuʒnā > kogna > coun > Ilk. caun (Ety/KUƷ). There is an identical (and equally peculiar) phonetic rule in Old Noldorin. What makes this change so strange is that the [g] produced by it would revert to [ɣ] when voiced stops spirantalized after vowels. This change could only be detected by comparison to Danian, which seems to be the only language in this region that would preserve a post-vocalic [g] (Dan. cogn, Ety/KUƷ), but it could just as easily be explained as a change unique to that language. Assuming the rule is valid, it would also apply to ᴹ✶doʒmē > Ilk. daum.