You probably realized how Krešo did it at the moment: approximately, the ships are a few "units" above the background (on the Z axis) and that's it. We definitely plan to rework the whole thing since one of other side effects is that you can fly outside the background and into the "white space".
We will consider what to do.
But if we went for realism -- the background should probably not move below the ship at all

Obviously, for this game, realism is a no-goer (just like for 95% of games)