I don't know what you mean by "normal setup". Anyway, according to the tower tutorial two "compute terrain" are needed because otherwise you DO NOT get any displacement on the tower surface. At least not using this method.
I'm not an expert Ulco, but if shadows and sunray-through did not require any special actions to be taken like you say, there would be no need for the "receive shadows..." option... Still, it just doesn't work with this rock tower...