Heat Pump Math Question

Hi HVAC, we are thinking about installing a heat pump and an HVAC tech mentioned to us that the inverter runs no less than 20% power.
So let's say for example.. we have a 36000 outdoor unit running to a 12, 18 and 9 unit inside our home.
So for today, the only unit that is on inside the home is the 9 in the bedroom for Grandma.

Once the 9 unit reaches the set temperature it will then dial back the inverter outside to slow down.. but since the inverter can't run less than 20% of 36k or 7200 BTU worth of energy, then the 9 upstairs will never be able to dial back the inverter outside lower than generating less than 7200 BTU worth of power consumed?

Now, if the 9 in the bedroom is independent and running on a 9 outside, then the inverter at 20% would equal 1800 BTU when the 9 is it's running the inverter at the minimal 20%.
I'm not sure if this math is correct or not or if it’s true that the inverter runs no less than 20% power?

I want to make a decision on whether to buy one outside 36unit or go with multiple units such as a 12 & 9 &18..

Thanks

source https://hvac-talk.com/vbb/threads/2239263-Heat-Pump-Math-Question?goto=newpost