TL;DR - heat set to 70, room temp slowly falls and doesn't catch up. Bump the setting to 80 and it catches up quickly.
The house is a ranch style 30'x60' with R30 insulation in the ceiling. The outdoor unit is a Mitsubishi MXZ-5C42NA2-U1 with 43,216 BTU cooling and 19,464 BTU heating. Three bedrooms have MSZ-FS06NA-U1 installed, one has MSZ-FS09NA-U1 and our great room (25'x30') has a MSZ-GL18NA. There is 1 bathroom and a small office without a head unit installed.
Now for the long winded post. I have a multi head set up with the main issue being a Mitsubishi MSZ-GL18NA unit. This unit is installed in a 25' x 30' great room with a 12' vaulted ceiling (no attic). The company originally ins