I do not know if this is the mechanic of this kind of game, but if you start a free fall, just dodging the enemies and do not killing them, they start to chase and acumulate on screen and that make the game so hard.
maybe, if you gain some distance, the enemies rest behind and dont chase the player. do not need to be all the kind of enemies or put different distances for each kind of enemy to stop chase the player.
also, you could put some bonus for finishing the level less than an predicted time or/and without killing any enemy.
Thanks nemezes, the current range for Line of sight should be around 500 -1000, I will try to reduce it base on each monster.
I am still thinking how to implementing a good clear bonus, It is in my TDL.
As for non kill bonus, it quite impossible.
Thanks for feedback~