Question about be quiet! Dark Base 700

According to the manual, you can also install a fan in the bottom of this case. I have Silent Wings 3 from be quiet! But unfortunately I can't install them at the bottom because the screw holes are too narrow. In addition, only two holes are easily accessible from below (without dismantling the front). Am I missing something or is it a faulty design? Or does the fan not belong at the very bottom, but at the height of the front, removable "power supply plastic panel"? Thank you for your advice.