You're confusing yourself. Right now if you're in a fireteam and you leave at the first checkpoint (confluxes). Everyone has that checkpoint at the confluxes. If you start a new fireteam where you are the leader then the whole group will start at your checkpoint. However, if you join another team where the leader has the next checkpoint (oracles) the whole team will start at that checkpoint. Basically everyone gets the checkpoint but the leader's checkpoint dictates where the fireteam will start.