I know it's only one datapoint but recently we had four indoor airco units installed in our house for the bedrooms and livingroom. I expected a single outdoor unit. However during talks with the installer he advised us to go for two outdoor units. This was cheaper in hardware, a bit more efficient and way cheaper to install by placing one outdoor unit on the front of the house and one on the back so all rooms could be reached within a meter or so from the outdoor units.