PIE suffix *-so

Please if you could help me with the possible meaning of the PIE
suffix -so

I try to explain Romanian ceafã 'nape' <-> Alb qafë 'id.' as PAlb *kep-
sa < PIE *kep-so where *kep seems to have the meaning 'head' and -so
seems to indicate somehow 'a location nearby the head' but I'm not
sure about its nuance.

Thanks a lot for some similar examples reflecting (the meaning of) *-so

Marius