Comparison between modelled (solid line) and observed (dashed; same in all panels) line profiles towards a position 20 au north of the protostar. a) Model free-fall line profile towards a 0.1 M_⊙ protostar; b) Free-fall line profile towards a 0.4 M_⊙ protostar; c) Episodic infall towards a 0.1 M_⊙ protostar; d) Episodic infall towards a 0.4 M_⊙ protostar; e) Streamline infall along cavity walls towards a 0.1 M_⊙ protostar; and f) Streamline infall along cavity walls towards a 0.4 M_⊙ protostar.