The centerline forebody pressure profile, as far as any potential 'thrust' was concerned, would have to be considered within the context of the vehicle's entire pressure distribution, and not just centerline, but the entire body surface area.
An easy example would be the HUMMER H-1, which would demonstrate a remarkably low pressure spike over the grille-to- bonnet transition ( more dramatic than the Prius ), however that spike would be overwhelmed by the lack of any significant roof camber, and then premature separation off the back of the greenhouse, where the local pressure at the separation line is virtually the same as the lowest pressure on the HUMMER, at the windshield-to-roof transition. This super-low pressure would telegraph all the way across the rear, to the base, where the negative low base pressure would completely overshadow any potential ' thrust' at the forebody.
The reason for its Cd 0.70.
Laser Doppler Anemometry is one technique available, which can scan an entire vehicle surface, to ascertain all spatial local velocities and static pressures, from which the whole-car pressure distribution can be derived.
It's not an easy thing for us, especially if vorticity is present, virtually impossible to visualize outside of a laboratory.
