Above 400 points and it goes far down. At 500 points you have far more ships and a higher likely of chance ships being destroyed. This means that 15 points a token is a tiny drop in a bucket. It is no longer 3.5% of your points which sounds like a tiny portion but can be huge when trying to figure out the deferences in a win or loss
This is why the game is tested and optimized for 400 points.