What's a reasonable COS score when filter is set to pessimistic?

Hello,

My plan gives me a 88% COS when using the average filter for rates, but it drops down to 12% when I switch to pessimistic. I'm wondering what is a reasonable score when using the pessimistic filter? I'm thinking it shouldn't be too high as you would more than likely would be living and budgeting under your means and leaving a lot of money behind. I'm good and confident with an 88% COS using AVG filter, but the pessimistic 12% COS gives me pause. Thoughts?