You have already highlighted all the main reasons it's cooling isn't chill enough.
I have viola in parents room on ground floor at the back where it gets absolutely no sun from any where, room is usually cooler any way, they put it at 28c but rooms feels chillier than my room set at 26c which is smaller but is at the top floor and gets full sun exposure from 2 walls and the roof.
In our basement we don't we need Ac, just the fan is enough.
Also, compared to conventional Ac inverter take a little longer (few mins) to cool the room.
Gree has gotten very expensive this year, almost cost same as lg and samsung. How much did you pay for viola this year.
