Ahh Heatseeker, you have jumped to too many conclusions. I have a 20kW loadshedding generator up here on the mountain, so when we experience protracted power problems, I can trip the breakers to the electric aux heat. That allows me to continue to run the heat pump on my generator for whatever heat it can extract. Ambient up here was in the mid 40's when I collected the temp/time history on the heat pump. The outdoor unit (RPNE-060JAZ) ARI heating design specs include data for 47 F (dry bulb) and 17 F (DB), so the unit was operating well within its performance envelope and no aux heat would have been called anyway.
Your initial reply sort of confirmed my thinking about what the temp history ought to look like. I'm beginning to think my unit has a slight refrigerant overcharge - within spec, but just a bit more than needed.
Thanks for your input.