Having all the ghosts behind you gives you more control since they'll follow you in a line.
That the ghosts follow the player is what makes the game winnable. If they formed a grid and gradually closed-in, it would be impossible to escape.
Edit: What was unexpected in this case was that the system found a strategy the programmer didn't think of.
For example in EVE Online with a 1v1 fight two basic tactics are either Kite or Brawl. A kiter that can maintain range will beat a brawler. But a brawler that 'catches' a kiter will generally win.
Having all the ghosts behind you gives you more control since they'll follow you in a line.
That the ghosts follow the player is what makes the game winnable. If they formed a grid and gradually closed-in, it would be impossible to escape.
Edit: What was unexpected in this case was that the system found a strategy the programmer didn't think of.