Positioning of some Modifiers

mauro sacchetto

A question on a lesser-known topic, on which I haven't been able to find any information: the positioning of some modifier glyphs, such as the Modifier Letter Centered Right Half Ring (U+02D2) and Modifier Letter Centered Left Half Ring (U+02D3) pairs. I should point out that glyphs like these are completely absent in many fonts.

As always, before posting my question here, I checked the settings for some fonts.

GNU Free Serif places the glyph roughly at 0 height, that is, close to the base of the other glyphs:

Brill, on the other hand, places it roughly halfway along the x-height:

What's the best solution and the logic behind these cases?

Thanks

m