What a LoL split soft reset actually does
A split reset is a soft reset, not a wipe back to Iron. Your visible rank drops a step and your in-division LP resets, but your hidden matchmaking rating carries across, compressed toward the server average. That carried rating is the anchor: the five placement games read from it to re-confirm where you belong, which is why two accounts finishing the previous split at the same rank can still seed differently based on their hidden ratings. The table above lists exactly which parts of your standing move and which ones the placements settle.