Ideas:

1. Another possible way of thinking about the time of new moon is to regard the disappearance as an optic effect: It is because the moon is gradually turning away its face until we see her dark side.

The back, the dark side, must be opposite to the side where the face is.

On the side opposite to the face there are no eyes, just a lot of black hair.

2. In Tahua (Ab1-16) Metoro explains that this type of glyph is showing a kana rei, the shell inside a hairdo for women (Pouo).

3. It is intriguing to consider that Bishop Jaussen received the rongorongo tablet Échancrée completely enveloped in human hair, i.e. hidden.