A aṅga (stem) ending in o loses its final before the Present characteristic śyan of the divādigaṇaḥ (4th Conjugation).,
As मिश्यति from शो, अवच्छयति from छो, अवद्यति from दो, and अवस्यति from सो ॥ The त् in ओत् is for the sake of euphony or ease of pronunciation.
According to Padamanjari, the sutra should have been ओतः शिति, and thereby there would be the saving of half a matra, and also there would be no necessity of repeating the word शिति in 7.3.75.,