Ty's probably right.
Though it's hard to say for sure for every specific vehicle.
The good news is a temporary air dam is relatively easy to make, so you could A-B-A test one yourself to see if it works.
FYI, Big Dave has a significant air dam on his Ford, though its ride height is much less than yours:
http://ecomodder.com/forum/showthrea...ckup-3171.html