You mention that FSRS treats each card independently, even if they derive from the same note. I wonder whether you've tried this Anki plugin, which tries to increase the interval between reviews of 'sibling' cards: https://ankiweb.net/shared/info/759844606
Since in Anki the "note" is the editing unit, that works for some cloze deletions but not for QA cards (only for double-sided QA cards). A content-aware memory model would allow you to apply "disperse siblings" to any set of cards, independently of whether they were created together in the same editing interface.
