[Cd]

How does one know if a design that falls out of the traditional teardrop shape truly has attached flow in areas that are suspect, or if what we see is the result of the Coanda Effect ?
I'm guessing that the Coanda Effect needs some sort of additional surface outside if the main bodywork that the air sticks to. So the effect could be possible if induced by a gapped spoiler device, but not on a car without it. ( Example : something like the spoilers at the edge of minivans that has an air gap that draws in the air and sends it down the back window, versus a car that has no spoilers. )
Would this assumption be true ?

Edit : On second thought, I have seen a video of the Coanda Effect, in which a guy places a wine bottle in front of a candle and blows the front of the bottle which has the candle behind.
The air flows around the bottle, and blows out the candle.
No additional planes are present around the bottle to create this effect, so it seems this effect could be present without the use of (ducted ) spoilers on a car, and the effect could be seen over a normal roofline.

I'm so confused.