Was the insulation being important realization related to the mini split install? Curious why that would be more noticeable with mini splits vs other forms of heat.
Capacity. Heat pumps are typically lower capacity (in BTU/hr delivered) than a fuel burning appliance and that capacity drops with very cold outside temps.
Sounds likely, however this is also my first winter—and my first cold sprout—with them, as such I’m learning which temperature to set it at etc. With our gas stove we usually set it higher on cold days, I guess with heat pumps we need to do that even more so.
Inverter drive heat pumps do well in a continuous and lower output situation, so the conventional wisdom (from gas fueled appliances, often with only 1 or 2 stage burners) to do a nighttime setback for economy is less useful economically. Set back for nighttime comfort if you want/must, but not (much) for economy.