Mid-engine Diesel. i can‘t say I noticed any change. There is a satellite dish dome right in front of the panels, two acs and two vents etc so it was fairly turbulent anyway. 6.5mpg before and after. The panels are more “knife edge” and present a smaller edge than the panels I had puzzle pieced around the ac units. First photo shows the difference as I began installing them. I have thought about a dam, but mainly to keep branches etc from getting caught under.