Zompist Bboard Again

I could see coronals patterning with central vowels considering different analyses of Mandarin syllabic fricatives (i.e. [ʂʐ̩] vs [ʂɨ]) and the Index Diachronica lists PIE to Proto-Tocharian with n̩ → ə → ∅ / C_#. And I guess /a/ can be central, but I don't see it with other low vowels. Where did yo...