[aerohead]

My takeaway was:
1) the significance a vehicle's aft-body to overall drag. IF that WAS a Model S Plaid, then we'd be comparing Cd 0.208, to Cd 0.599- 0.598.
2) the importance of monitoring air density during testing, in order to attribute any delta-Cd to an aerodynamic modification, and not 'thicker' or 'thinner' air, as weather changes during the course of testing.
3) at the sister Aerodyne Wind Tunnel, they have the facility to feed 120-pressure tap readings, simultaneously, from any body panel, with no chance of pressure 'drift' during data capture. At this level of resolution, an isobaric contour map can be generated for a 'deck', backlight', 'greenhouse roof and quarter windows', etc., allowing a more 'complete' picture of what a specific mod is doing, as NASCAR does. Very important considering rotational, incompressible, subsonic flow, where any mod, anywhere can affect local pressure at any other part of the body.