Compressor housing A/R?

[iTurbo]

How does the size of the compressor housing A/R effect turbo flow? Does it all depend on which compressor wheel is being used?

[MachineHead]

The biiger the housing the more it will flow, but the slower spool up. It works the same on the exhaust side. The higher the A/R number the larger the housing. For example a .63 is bigger than a .48 turbine housing and a .60 is bigger than a .42 compressor housing.