I don't believe that it does cap the range. I see it as:
At least x (where x = 10-20). X is the minimum, and you can always exceed it, whether it is a single value or a range.
If you bake 100 brownies, you satisfy the requirement of baking at least 10 brownies, as well as the requirement of baking at least 10 to 20 brownies.
If you bake 100 brownies, you satisfy the requirement of baking at least 10 brownies, as well as the requirement of baking at least 10 to 20 brownies.