For residency schedules, it's often best to balance just the days you're filling, such as one rotation. If you set up the block schedules properly so that people are available to the call pool for the same number of months throughout the year, you'll be assured that total calls will be roughly even by the end of the year.

Go to File / Preferences / Autoscheduler you'll see two options: select Balance totals for year or Balance totals for just the days being filled.