An aerosol-generating system includes a liquid storage portion including housing holding a liquid aerosol-forming substrate and a capillary medium. The housing has an opening. A fluid permeable heater assembly includes an arrangement of electrically conductive filaments arranged to define an air impingement surface. The fluid permeable heater assembly extends across the opening of the housing. The filament arrangement defines a filament opening allowing airflow to pass through. The capillary medium is provided in contact with the heater assembly. The capillary medium is configured to draw the liquid aerosol forming substrate to the electrically conductive filament arrangement. The capillary medium includes a capillary medium opening extending the filament opening through the capillary medium.