The affix ghañ comes after the verb nī 'to lead' when the prepositions ava and ut are in composition.,
As अवनायः 'throwing down'; उन्नायः 'elevation'.
How do you explain उन्नयः in उन्नयः पदार्थानाम् ? Here the affix is 'ach' by 3.3.113.,
अव-उदोर् नियः
Adhyāya 3 · Pāda 3 · Rule 26