I've only played the Throne Room level once, and he spawned in the west. My friend says he spawned in the west for him as well. Two trials is hardly enough to go by, however. If I want to play the level again and set up extra defenses facing west and he comes from the east, I'm going to be in a bad spot.
I ask because the same thing happened to me with the ogre in Foundries and Forges. He always moved and attacked the crystal from the east until I set up all my defenses once facing east, and then he moved to the south entrance instead.