Let's make triple the size with the same count in each as there is today. In a circuit court if the decision goes against you, there is always the Supreme court. So, should one have the option of appealing a SC decision? As in ask for a different group of Supremes to consider the appeal?
In the circuit courts, there's already recourse. Appeals are generally heard by panels of three judges. Most of the time, that's the end of it. But if the appellant or appellee isn't happy with the result, he or she can ask that the court consider the appeal en banc, which means that all the judges on the circuit would be involved. It doesn't happen all that often--and the full court doesn't have to agree to it if it doesn't want to--but it's a possibility.
It could work the same way for an expanded Supreme Court.