It has been awhile since I played the game, but from what I remember, the paragraphs determine the open/close state of the tank. I don't believe that once a tank was fired upon, it automatically closed. I do remember it was a tank's action, to close when instructed by the paragraph, which could have resulted from being fired upon.
Often (not always) the tank paragraph will lead with "If this tank has been fired on..." or "If there are (x) targets visible then button up", otherwise follow the paragraph. Doing anything not specifically called for (no matter how logical) will cause problems with the mission program.