Here only A and B are in cover because: 1: The Red Circle Guy can't see the whole square. 2: A and B can move 1 non-diagonal square to be 100% out of sight. So the A or B gets a saving roll, allowing them to duck around the corner.
Cover on Corners: If you get shot and you lose a life point, but you are "In Cover" (see above), roll a white die. If the result is 1 or 2, 1 lifepoint is instantly restored. (Corners provides protection. So skillful tactical planning is rewarded. You could outflank your opponent so he has no place to hide.)
Comment, this reduces the "A-Team" nature of Space Crusade, where everybody just lines up and shoots each other. Now you can win the firefight by careful placement of your troops.
Edit: "Hour of Glory" - Killing Time 3 (2008) has a similar cover rule, except that cover doubles the firing range. Hour of Glory isn't entirely unlike Space Crusade, especially the BunkerStorm expansion.
Great minds think alike.