Apparently the tuning screw can actually become loose during shipping or by accident and it lead to crazy channel imbalances that the thread starter on the site I mentioned measured with his measurement rig. I don't know how common it is, but I do know that Dan was having conversations about the tuning/channel imbalance issue with that individual. The tuning screw is used to adjust the port so it can have an impact on the sound. Please note, I have no first-hand experience with this, but it was the topic of discussion and there were images of the screw in the port so it is certainly at least a design feature. Hopefully Dan can chime in here and offer some input into things.