An aerosol-generating system including a cartridge is provided, the cartridge including a liquid storage portion including a housing configured to hold a liquid aerosol-forming substrate, the housing having an opening; and a heater assembly including at least one heater element fixed to the housing and extending across an opening of the housing, wherein a width of the at least one heater element of the heater assembly is smaller than a width of the opening of the housing. The heater element may be spaced from a periphery of the opening, leading to more efficient heating and aerosol production.