The smaller the diameter of a cyclone, the faster the air must move and the better the separation. Likewise, the smaller the cyclone diameter the larger the blower needed to overcome the resistance. It takes more work to push air in smaller circles. Cyclones with longer cones provide better the fine material separation. Likewise, longer cones create more resistance because the air has to run more revolutions. You can compute a near ideal cone length for maximum separation efficiency based upon air speed, inlet, and cyclone diameter. Finally, the larger the cyclone outlet, the less resistance and slower the airflow making for much finer the separation.