The overlap of the ring current with the outer plasmasphere is thought to play a major role in storm-time related increases in the subauroral ambient topside electron temperature. Instabilities generated within the overlap region, Coulomb collisions of plasmaspheric electrons with the ring current ions, and charge exchange are all thought to work either individually or together to generate a downward heat flux into the ionosphere to produce the increase in temperature. Analysis of IMAGE two-dimensional ring current and plasmasphere density maps together with in situ DMSP ambient electron temperature data shows that the heating generally occurs over a small radial extent within the plasmasphere/ring current overlap region and may be significantly earthward of the plasmapause. This argues against collisional heat conduction as the source of the heat flux and for an instability-based process. The finding that the heating occurs within well-defined ratios of the cold plasmasphere to hot ring current density strengthens this supposition.