As part of configuring a Display Template, you can choose the fields included in the Sort list as well as their relative precedence.
To Configure the Sort Template:
Field Hydration is measured as the percentage of records that have a value for a particular field. You can use this measure to see which fields would be more effective filters (high hydration values) and fields likely to be less effective (low hydration values).
To see the Field Hydration values, select a Saved Search under Test Field Hydration and click Run.