I see the various aspects of this......here''s what I
SEEM to notice about blocking, diffusing & such.....
Something like Hogsy's setup, or the cheap version using aluminium foil.....funnels the air toward the coals.....I've seen very old long time kettleheads use foil & trays / pans & such to do that....just because it occurred naturally to them & because they don't like to clean shit up out of the bottom of their kettle as much as i do.....
What Troy's saying about stale smoke could happen, I suppose, but likely on a very slow cook where the temp isn't high enough to keep things (air) moving......it's much more likely to happen in an offset.....not sufficient draw is the terrible nemesis there......
In a kettle, with a pan or tray or foil, follow the arrows in that diagram........you also see blue arrows, I assume indicating cooler air......granted, that is somewhat of a factor, however, the pan/ foil/ tray WILL heat up.....just like the rest of the "metal in the kettle" & provide some cooking heat of the other type that Gummi & Troy are talking about.....
The kettle is a perfect design......the air circulating is just like the Jet Streams around the Earth......