[M_a_t_t]

Originally Posted by jakobnev

If the flow is upwards over the rear windows, could it be creating trailing vortices?

May i propose bringing the rear deck up with something easy to make that wont obstruct you view:

I wasn't sure who's car you were referring to with the first comment, but I had been thinking about adding a tall spoiler/fence to see what happens on the back window and will add the taller decklid to the list.