I’m not sure how I can explain it even more clearly:
OGS uses one single sole individual rating system for ALL board sizes and speeds.
You keep hammering on 9x9 being ignored: it’s not. It’s not getting treated differently than 19x19. It counts just as well for your overall rating. All three of 9x9, 13x13 and 19x19 board sizes and all time settings are included in the rank calculation.
Handicap stones are distributed differently for 9x9 than for 19x19, so 1 rank difference does not equal 1 handicap stone difference. Instead a conversion formula is used. That’s all there is to it. Whether this is accurate, is something @gennan discussed above, but I don’t believe this is what is bothering you.
This has nothing to do with each other. Nowhere in the computation does Glicko use anything other than who won the game and who lost the game. Board size is not a part of Glicko.
If you’re confused about what Glicko is, just replace it with “Elo” whenever you see it, and the story will be completely analogous.