Cost value in HFSS Optimization result

Dear all,

I am designing a Radome design with HFSS optimization function.
My cost function is as the attachment "Capture1" image:

My goal is the magnitude of S21 is over 80%.
So the function is: (S21)^2 * 100.

But in the optimization result, I got as the attachment "Capture2":

I do not understand why the "Cost" value is so high, around 5000. Please help me to explain this.
I had tried to find the document from Ansys but not successfully.

Thank you so much for your consideration!