Some people seem to want to liken this to a theater, allow me to point out the flaw in this logic. We are not going to watch some entertaining show, we are there to whoop the ass of a giant, ugly space monster. Therefore we are not entering a theater, we are walking onto a battlefield. On a battlefield the enemy comes from the front, during this encounter, Oryx and the majority of the other enemies such as the thrall and knights that are the first wave come from the front, even the tomb ship drops the vessel at the front. Oryx spawns in at the front, that is all there is to it.