[aerohead]

The existing locked-vortex is already 'streamlined' in form,looking just like an aeroshell.
Allowing the vortex to 'communicate' under the half-tonneau to the inner face of the tailgate is also of some importance,as it provides a pressure differential from front to back across the gate,allowing some thrust and is part of the streamlining criteria of the wing/half-tonneau system.