If you are going dead slow (which you may be in very limited visability), then the beam will be close to parallel with the lines of the cabin top. If you are going at displacement speeds--up to semi displacement speeds, you may be up 5 to 8 degrees--and at a plane you are often at a bit of an up angle. However, I have always installed my radars parallel to the cabin top, and found that I had good radar visabilty at all speeds. Theoretically the down angle of 5 degrees could be justified.