An aerosol-generating device including a cavity configured to receive an aerosol-forming substrate is provided, the cavity having: a first end and an opposing second end, a length between the first end and the second end, and a cross-section perpendicular to the length, a perimeter of the cross-section of the cavity remaining substantially constant along the length of the cavity, and at least one of: a shape of the cross-section of the cavity varying along the length of the cavity, a surface area of the cross-section of the cavity varying along the length of the cavity, and a dimension of the cross-section of the cavity varying along the length of the cavity. An extractor for extracting an aerosol-forming substrate from the aerosol-generating device is also provided. An aerosol-generating system is also provided.