Hitting the underside of the umbrella valve and falling back into the sealed cavity in the middle rocker box.
From there it should drain back into the lower rocker box through a tiny hole behind the umbrella valve.
This tiny hole is in a recessed area behind the umbrella valve.
There is a certain amount of backpressure in the sealed cavity away from the air exit hole.
This backpressure should help push the oil into the tiny hole and back into the lower rocker box area to be carried back down to the lower end.
The upstroke of the pistons causes a vacuum to form in the system.
This vacuum is also pulled through the oil passage from the heads / rocker box.
(in theory, it should help pull oil through the drains in the heads to the bottom end.