This looks like it might be a case of "can't tell without A-B-A-B testing" since the underside is already so smooth.
I don't have numbers to back it up, but I've always been under the impression that having an airdam with the bottom edge level with the lowest point on your undertray (i.e., no lower than any point on the non-suspension parts of the car) is best, and to keep the tray level from there back to at least the rear wheels. Seems to me like having it level in front would be better than wedging more air under the car. And I think I recall hearing that it's better to have the stagnation point on the front of the car lower than higher, and the airdam would lower the stagnation point.
But I don't know. I too am not eager to duplicate work just to test.
