As seen in this video in the exterior (not cave) there are smoke hits where there should be a rock and the guy supposedly getting shot does not seem to have any animation or blood of getting hit.
https://www.reddit.com/r/dayz/comments/1g2f3fk/_/

As seen in this other video, there are smoke as well in the middle of the tunnel or cave where there aren't any rocks in the way and the guy don't get hit until the third shot, so this hints too for very bad rock hit box.
https://www.twitch.tv/joito/clip/EsteemedInnocentNoodleUWot-90JgIHw-KvByPeKT