Hmm... Well, if I go through the situation, I hope it helps :)
Illumina is running towards the mountain cougar that just jumped towards her to get around Lyra who just launched a death beam. Whether it hits or not is still a question. The cougar has a direct line to Säätur who tried running but fell. With just a couple of leaps the boy would be dead. Steven has his halberd ready and is running towards the scene.
But the truth is, if the cougar leaps at Säätur, Steven might (not) make it. The death beam then won't hit it's target. Illumina is closer than Steven is and the cougar has it's eyes on Säätur.
As I said, I hope this helps a bit ;)