Prime, as the members responded, you can see this installation right on the Great Grady Home Page, it's a Sailfish, but the idea is the same.
The radome sends out a beam angle that is typically 13 deg. up and 13 deg. down off the horizontal (mounting plane of the radome). Even if you have rod holders up there, other antennas, etc., the scanner will see fine as it sweeps 360 deg. around. And the actual antenna in the radome is in the upper half of the radone, so the lower half doesn't need to be in the clear.
I' have two GPS mushrooms, and one satellite radio mushroom in this beam, never had a problem. I just keep it away by about 2 ft.
And when the boat is sitting moored, the scanner should be level to slightly pointed down in the front, so that when the boat is off plane with bow up, the scanner sees in the water the closest to the front of the boat it can. You can buy wedge blocks sold for this purpose to change the angle if needed.