Basically. I live in a ranch that is on a hill.
My Garage is in my basement. I also have 1/4 of the basement finished. Its about 300 square feet.

My house is a little under 1200 square feet.
I've had two quotes and both seem to think 2 ton heat pump, 2.5 ton air handler and say the finished room doesn't matter.
The finished room does have 2 heater vents in the ceiling.

here is a quick drawing of my basement



To me it seems like the finished room would count for some kind of heating and cooling usage.... granted it does stay nice and cool in there in the summer but it does get a little cold in the winter