It actually doesnt lower the front very far at all, from what I can see. The lowest part is where it hooks onto the lower wheen arch just in front of the wheels (where the liner meets the bumper), and even then it is only by the thickness of the actual CF, so a few mm at most. It also doesnt stick very far forward of the centre of the bumper, only about an inch, but where the bumper normally curves back towards the wheels, the lip protrudes forwards more which I think causes the problem.
As it sticks out quite far forward at the sides of the bumper, it does mean that you have to be careful with slopes. I used to take them at an angle but that doesnt work any more. Other than this one awkward speed bump into my close, the other 3 are fine and can be taken at normal speeds, its just this last one that I have to do in first gear. Phil has said he doesnt have any problems with his and clearnace, I just think I have a dodgy speed bump by me!