I'm not sure if you've ever created a mission or not, but it takes an daunting amount of work to get an entity to block that up there. It requires them to mess with the PBO, and for something as silly as that it's simply not worth it. Would likely look bad, and would take damage separately.
The world-building language Arma 2 uses makes next to no sense at times, for example: player setPos (player modelToWorld [0,0,10]); ... Now looking at that, that's one of the potential commands for such an item if you replace 'player' with 'this', that you could place, and would have to place, directly overhead. You would then have to use the X,Y,Z axis to put in the proper place, and that may very well require decimals to make it look semi presentable (I once had a mission that had a 3.05333339 in place of the '10' in the example to make the entity work as intended). Also of note; while they work on something as trivial as this, they may be the only staff online when there's someone hacking away on the server and ruining everyone's day.
You can't necessarily shoot out of that in any case, only peak- and peaking there is very dangerous for lack of cover. I don't see how it's any worse than rocks you can hide inside/under. You have to realize it's not that easy to edit a mission for this game, and I'd rather the development staffers devote their time to more pressing, game-breaking issues.