PROBLEM

Hello, @imedabolkvadze!
Sorry for the long time without answer!
The discount is not 20% because you pointed the Max discounted sum $20. It means, that you give 20% discount, but the discount sum must be less than $20.
20% from $149 is $29,8, but according to your rule, your maximum discount is $20. Then the discount badge calculate the new percentage discount. For the product with cost of $149 your $20 discount is 13%.
Please, clear the field “Max discount sum” if you don’t want to limit the discount amount.