The fact that my co-worker saw a box I designed for a friend on Facebook and told me that it would sound like shit because the box was too square.
I looked him straight in the face and said alright man, and that was the end of that conversation.
I assume the 1.5 is after displacements, the level 3 12" displaces .16 cubes.
You could go with the usual 12-16 square inches of port per cube or try to optimize a port based on xmax of the driver.