The upper vortex is created at the top of the bargeboard and flows along its outline. This means the upper vortex slopes downward and contributes to the downwash generated by other parts of the car (including the profiled wishbones, the fins on the edge of the cockpit, etc.). The downwash flattens the airflow rising in the wake of the front wing.
As it goes down, the upper vortex moves away from the middle of the car and towards the flanks of the sidepods (where its interacts with the Y250 vortex) and leading edges of the floor. One can assume the energised air then travels through the slotted floor.