Ideas:

1. The concept of vaiora a Tane ('the living water of Tane') is important in Polynesian thought. It is the insight that all our lives depend on the Sun. And that the all essential sweet water is ultimately delivered from the sky, the abode of the Sun. Perhaps this type of glyph is showing a container filled with water placed over the Sun:

2. From the readings of Metoro it is clear that he usually saw oval types of glyphs as vai, '(sweet) water'.

3. My interpretations are congruent with an interesting parallel between glyphs in Aruku Kurenga (B), Large Santiago (H), Large St Petersburg (P), and Small St Petersburg (Q):

Ba10-16 Ha9-111 Pa8-45 Qa9-17

The Sun in the form of the Sun-bird implies water.