Also from ACI's site:

"When it comes to ducting, the number and sharpness of its bends factor into the airflow resistance. This is because airflow reduces the further it must travel so the straighter the ducting route the better. The sharper the bend, the harsher the efficiency reduction; a 30° bend cuts the amount of airflow by 20% while a 90° bend diminishes airflow by 60%! Smoothing out any wrinkles can also improve fan performance and airflow. If you are using LED grow lights, you must also account for its heat output which further increases your required CFM by up to 50%."

Thanks buddy, exactly what I was looking for.