"it should be just where individual singer feels it."
Not really Dick - it's where the song demands it. quote jim
   it is up to the individual singer to decide where the song demands it,
we may or may not like it, that is our opinion, however teaching ornamentation, and insisting that it has to be a particular way, stultifies the music.
Rachel Carstairs imo appeared frightened of doing the wrong thing, that is so wrong, Singing should have a "joie de vivre", a singer should not be scared or frightened of doing the wrong thing.