Regardless of where you stand and what you find to be effective, I would recommend letting the student continue to fret as close to the fretwire. At minimum, that is definitely the placement that requires the least amount of pressure to fret a note cleanly. It is definitely standard pedagogy for guitar, and you don't want to create a situation where it becomes you vs. his former teacher, as a teacher myself, that can be a source for students going in a different direction.