Can't charge restocking fee

Hello,

I am having an issue where I cannot charge a restocking fee for a particular return. It only allows us to refund up to 50% of the original order amount, but we want to charge them only a 20% restocking fee. I don’t know why some of my returns allow for the option of charging a restocking fee, while the others only allow for a “partial refund”. Please advise, thank you very much.

Regards,
FMS