What determines the difficulty level of the battle?
I understand that the map tier (Forest, Junkyard, Sanctuary) makes a difference. But within each tier, there is a wide variety of difficulty levels. In Sanctuary, I have seen between difficulty 27 and Difficulty 33. What decides the difficulty within that Sanctuary set? Is it the level of survivors from that 'opponent' player's roster? If so, does having level 33 difficulty on their maps mean that the opponent has 10 star survivors on their roster?