Yeah, I agree, you can do it either way, and until now and receiving the new dual vent door, I was a small opening on top, wide open on bottom kind of guy. In experimenting with the new bottom damper, I've been trying to hold everything but the vents constant for the last few cooks and have been watching more closely. I have noted that a breeze blowing across the top hat and really increase the suction. What can be a light colored smoke (not billowy, but not blue) can suddenly get blue / super clean with a pickup in the breeze. This has led me to the conclusion that, for my taste buds, the best setup is very small draft door opening on bottom, large opening on top -- BUT, I need to use more smoking wood in this setup because I do like a smokier flavor. I think I've decided I like the smoke that is fast moving across the food, and faster means more smoke wood, but not a lot more...and the beauty is, the pit temp still holds constant.
Fun stuff.