For what it's worth, this is on the Arecibo website:
Click image for source page.
Lucky to spot it with a parabolic reflector built into the earth that can’t be pointed.
Actually it CAN be pointed.
It is pointed by manipulating the feed-point/focus-point to look at only part of the reflective parabola below.
It is true that the only time the entire reflector can be utilized is when the target is directly in front.
The farther the target gets from 90deg the lower the gain.
For what it's worth, this is on the Arecibo website:
Click image for source page.