SAP Information Steward Is Unique rule with group by

I'm looking to create a rule that determines if a cost center shares the same hierarchy group (CSKS_KHINR), the Description (CSKS_LTEXT) should be unique and not have the same description as another cost center with the same hierarchy group. This seems pretty straightforward, as the Is_Unique function works, but not when I try and group it by the hierarchy group. Any suggestions?