Well, Amanda, my interpretation of that imbalance is that we, the viewer, are shown that Jack is obviously the more demonstrative half of the relationship. He's kind of all over the place, isn't he, laying out his plume feathers, so to speak? Perhaps we need some stability, some set background, to place him against, so that we can keep track. I think we're almost hoping that he grew up in an incredibly predictable, boring world. Which would explain clearly his gigantic need for excitement as sustenance. Ennis, on the other hand, plays his part so quietly, pragmatically, we really don't need to know where he's from. It's written all over him, by the way he turned out. Quiet, scared, lost, empty, searching, needing... I can see quite clearly without having to know the names of the towns, where these two boys came from.