If you go back to the Flowillustrator video
you will notice the green transition layer thickens noticible as it goes down the rear of the Beetle.
This may not be full seperation, but is causing significant drag.
A full seperation from a trip edge (ie "Herod's Helper") will cause less drag even though there is more turbulance.
Turbulent seperation provides force at a small magnitude in many directions while a thickened transition layer provides a larger force over an increased area, half of the rear of the car.