[ERTW]

I will try that george. Have you seen the hot rod bonneville 1980 camaro with a Cd of 0.21 as tested at A2 wind tunnel? The last gen infinity G35 aero kit used a spoiler Cd 0.27.

13° kamm back
Cx 0.329
Fz 377 N

15° kamm
Cx 0.328
Fz 412 N

Elliptical spoiler 2" tall x 56" wide
Cx 0.304
Fz 231 N

Elliptical spoiler 4" tall and 69" wide
Cx 0.331
Fz 98 N

The last configuration has virtually the same Cd and only 22 lb of lift...
I interpret the spoiler's domination over the kamm tail is this: the kamm tail has low pressure over a large area - hence the high lift. the spoiler creates a high pressure over a large area - hence low lift. imo, the kamm needs to taper the sides to be effective.

We've seen the "virtual tail". I propose the concept of the "virtual body" (it's all mine, never been thunk up before). The streamlines skim from the roof to the top of the spoiler. I'm investigating spoiler width to manage side flow (and vortices).