[aerohead]

The center image,illustrating the trailing vortices does not share the same roof width,or tumblehome of the roof for the first and last image.------------ This would affect spoiler performance,as in the last image you can see that the width of the roof as measured at the base of the rear windshield is much narrower compared to the center image.----------- The airflow at the trunklid would be completely different and consequently,spoiler width parameters would also differ.-------- It's a subtle difference,but it is still "apples and oranges" to the air.------------- The trick for the spoiler,is to get top and side air to merge at similar velocity and pressure,so as not to spool up into the drag-producing vortice.