The Billiard Congress of America defers to the World Pool-Billiards Association for the definition of a proper 8 Ball and 9 Ball rack.
The placement of two balls is all that’s required for a proper 9 Ball Setup.
According to the World Pool-Billiard Association, a proper rack for 9-Ball is:
“2.2 Nine Ball Rack”
“The object balls are racked as tightly as possible in a diamond shape, with the one ball at the apex of the diamond and on the foot spot and the nine ball in the middle of the diamond. The other balls will be placed in the diamond without purposeful or intentional pattern.”