In this case, "sponsors" is an extra tricky word, because in English you can say "X sponsors Y" or "one of Y's sponsors is X", and you can't tell from just the path which one was meant.
Good callout! Using verbiage like "sponsoredby" or "sponsorof" in the url could help clarify the relationship and make it read more literally, i.e. to answer "does marcus sponsor marc" you could use meta/users/marc/sponsoredby/marcus or meta/users/marcus/sponsorof/marc.
Yeah, I used "fund": 1 in the user/user/marc/marcus... then you just have to decide the direction and everywhere except arabian it's left to right... so marc funds marcus.
And user/user/marcus/marc has it if marcus funds marc.
