Cover v. concealment
The former not only hides you, but also offers some protection. The later only conceals you but offers you no protection. Here's a tidbit from the past that illustrates this lesson:
During the advance of Evans' Brigade across the wheat field from the end of Brooks' Hill to the Thomas house, a Federal soldier fired at the advancing enemy from bheind a wheat shock. The man himself was not visible, but the smoke of his rifle was. Immediately the guns of many Confederates were turned upon that particular wheat shock, and when the Confederates in their onward go, came to the shock of wheat, the Federal soldier lay there dead with a dozen bullet wounds in his body.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!