depending on how big the box is, power your using and what freq you want to produce.
depending on what subs your using.
from what ive seen at rms typical results are:
larger ports peak higher but peaks steeper
larger boxes pulls the band to lower freqs (to a point)
smaller ports are easier to generate lower freqs
again this is what ive noticed but different subs will yield different results.
atomic apx is one of those that threw me off. i got better results with a large box with smaller ports vs. smaller box with larger ports overpowering it.