Cool, well there we go then. You may have had the wrong reason, but it's still a good arc. Besides, modders could do some interesting things with it.
I was wrong about them being used against planets, though -- R9.23 says it was designed to assist in attacking bases. The player had to decide the arc before the scenario started, and then declare it when the first hellbore was fired. Actually, it's not very clear if each hellbore could be fired in a chosen direction, or if all of them had to point the same way.
I don't see it as a big issue if they are allowed to use both sides -- just give it a slight BPV bump.