Sindarin Phonetic Development (Part 26)
OS. [j] became [i] after vowels; [VjV|-Vj] > [ViV|-Vi]
It is well known that non-initial y ([j]) became vocalic [i] in both Sindarin and Noldorin. This is reflected in its spelling system, where i represented a vowel in the middle of words, but y at the beginning of words: