General rules for air cooling....
Air goes in the front, out the rear.
Air goes in the bottom, out the top.
Try to keep airflow in 1 direction only. Either front to rear or top to bottom
Watch for dead air spots that trap heat.
Try to equalize in-flow with out-flow. If you have 120 fan going in, make a 120 fan go out too.
Beyond that, using a fan controller to control your fan speeds sounds like something you should read about. Also, you probably are not using the best fans anyway. You should read up on the specs of your fans and how to use that to the best of their abilities.