The only issue I see is that after a while, people will stop playing if they don't have a great chance to earn any DEC at all. What if 10% of the Prize fund went to the top 10, and then the other 90% of the prize fund went to everyone in the top 50% based on cards killed? You could do 80/20 instead of 90/10. You could also do the top 40% or 30% instead of 50%. I think you get the idea.