Thanks for finding that out, @ianminds!
I’m experiencing that weird behavior right now, where studying more gives me a lower rotestock due to buried (but non-due) siblings.
This is not a subjective choice but probably a bug, right? I don’t think undue buried cards (learned) are supposed to count against the rotestock.
As for fixing the add-on metric, isn’t it super simple? Just remove the -is:buried from the search condition: -is:suspended -is:new -is:due -prop:due<=0.
With this fix, buried cards which are due will still be included due to the -is:due -prop:due<=0 conditions (so we cannot cheat by just burying the cards instead of studying). But buried card which are due in the future (and only buried because of the “bury siblings” feature) will not count against the metric now.
I tested it locally and made a pull request for that. Let’s see if @bluetulip agrees that future-due buried cards should belong to the rotestock and not count against it (after all, they are not due yet and assumed to be remembered).