Too-frequent defrost cycle? What’s the normal ratio of heat:defrost when it's this cold? – GreenBuildingAdvisor

Like everyone heating with minisplits in the upper Midwest these few days, I’m marveling at their capabilities. BUT, I’ve got one that’s not keeping up, and I’m hoping to hear others’ experiences. This unit runs for 30-40 minutes, then defrosts for 15-20 inutes. Given the long ramp-ups every cycle, I feel like I’m getting actual heat less than 50% of the time. With 0-10 degree outdoor temps, the unit can’t reach setpoint.

Mitsubishi SUZ 18K hyperheat outdoor unit paired with PEAD 18K concealed ducted handler. It was aggressively sized based on a study of the previous actual heating bills.

Even if it turns out it’s undersized by a bit, why is it spending SO MUCH time not putting out any heat at all? We spent up on the hyperheat model specifically to give us peace of mind on these cold nights. Any suggestions/compairsons would be most appreciated!