[MetroMPG]

Hi Novaz_nz -

My opinion is that the first spoiler renders the second one useless! It ensures that air coming off the roof has no chance of following partway down the rear window before separating. Instead, its slight upward angle will cause separation higher up and a larger turbulent wake.

However, I think there's a possibility that if you leave OFF the roof edge one, the decklid spoiler may be long enough to reduce drag, if flow off the roof can reattach on it.

Wool tufts hold the answer...