From research,it's been shown that an air dam directly below the furthest point forward on the nose,or slightly ahead will have the best drag and lift coefficients.
Here's a 'straight-down' version,it's too low for the street but good design
Here,on my truck you can see where the air dam is a little ahead of the nose,which gives it a bit of 'splitter' behavior as far as how the flow field is directed to the sides of the body
Both styles have the same Cd.If you let any air under the nose the drag goes up
