I don’t know whether this has been asked before, but I was unable to find it:
What is the formula for the endurance multiplier (at the end score)?
Does it have anything to do with the original amout of waves the level has?
 I have managed to find a topic about it, but it does not contain an answer. see here: http://www.kongregate.com/forums/76-gemcraft-labyrinth/topics/163738-whats-up-with-the-endurance-multiplier
anyone who does know?