Two recent studies of Lennard-Jones liquid-phase triple-point heat conductivity suggested very different nonlinear dependences of conductivity on field strength. This difference appeared to be paradoxical because the two calculations used very similar driving forces to generate heat flows. Here we analyze two sets of model calculations parallel to the Lennard-Jones work. The calculations describe a simple relaxation-time model for field-induced diffusive flow in a low-density gas of two hard disks. The nonlinearities found in the simple model suggest that the difference between the two Lennard-Jones conductivity calculations mainly reflects a difference in the comparable strengths of the currents studied. © 1985 The American Physical Society.