Why not give larger stones and so on the same positions like houses.
Then give the AI the knowledge from whrere the fire comes and where they are able to hide. This would help the AI to stop simplified falling down when they are under fires.

This could probably happen somehow like this:
1:AI mentions that is taken under fire (and mentions also the direction.
2:AI shoots some shots into this direction and runs into the next cover that allows them to be not taken under fire from this direction so easiliy.
3:AI engages Fire... informs team...

This can also happen with a house a tree chest..................... {F19832} {F19833} {F19834} {F19835} {F19836}