Are people in series usually grouped with other people in series for solo ranked?

I'm curious because the really absurdly toxic people seem to know when they can start the trolling in champion select before blatantly throwing the game instead of the more usual "everything seems normal until they AFK without explanation". At least one game per series (usually two) I get someone who seems to know that we can't drop out of queue because of series loss, which almost never happens otherwise even in bronze.