mike that fixed stand that the dome sits on and the pipe out the back that the cautus bracket fits over is a preset angle. availuble in 4,5,6" heights .just mount on top and your done.
A five degree down angle seems to work pretty well. Consider that most enclosed radar antennas have a 25 degree beam width. That gives you 12 1/2 degrees above and below horizontal. Add five degrees to that and you should have pretty good coverage even before you come on plane.