The length of the aft-body,divided by the actual body height (not including the ground clearance) is 1.5.
From Kamm/Fachsenfeld's FKFS research
,the car (shortest version) would be around Cd 0.25,and then lowered a bit due to the tumblehome,which the FKFS test model did not have.
Compared to the 'template,' the Prius has 37.5% aft-body truncation,which would predict around Cd 0.231,but we'd have to discount this a bit,since the Prius doesn't have as much plan-taper.
This is all at zero-yaw.
Cd 0.24 seems very plausible,especially since no counts are mentioned.