The command"Find Cover" implies, that a man will look for the most effective shelter. But unfortunatelly in the Arma3, for Ai units, this command is useless. in all cases, the AI will not seek shelter in buildings, even if it is close to them.
Example:
https://www.youtube.com/watch?v=VOcctYUZCe8&feature=youtu.be
At least a most units should take cover inside buildings (if the any building is nearby) But no one unit will not do this. @Bis, teach the AI use the "Find Cover" command is adequately.