Actually, you use the saucer as a "(heat) ballast," or "heat bank," and as a shield against direct radiance; but not as a "heat sink," which is something else. The idea is to keep a more or less steady temperature going in the cooking chamber despite variation in the in the fire pan; plus to ensure that the vast majority of energy in the cooking chamber is convected rather than radiant. Some popular alternatives to the terra cotta are fire bricks or sand. Many people use terra cotta shards from broken pots as a sort of "split the diff" between clay and sand.
The thing about using dry ballasts in the WSM (like kokopuff's) is that the WSM is incredibly tight as bullets go. The biggest advantage with dry ballasts is the flexibility they allow with temperature. Water in the pan really tends to keep it down because of how much energy it absorbs for phase change.
But none of those are good for RPM. He should use water or water plus aromatics (wine, beer, herbs in the water, etc.) in his ECB's pan because the ECB is so darn drafty compared to a WSM. A dry ECB is an unhappy ECB. :cry: (Not to digress or anything like that, but you only get a little flavor out of aromatics in the waterpan; what you mostly get is a great smelling backyard. Nothing wrong with that.)
Humid air doesn't strip as much moisture from the meat, and transfers energy more efficiently than dry (in effect "tuning" the pit and promoting even cooking). A WSM is tight enough that it keeps the same humid air circulating for long periods of time, introducing very little fresh, dry air. One measure, other than it's cooking, is its relative fuel efficiency. I.e., it's not pulling in a lot of air to burn a lot of charcoal, because it doesn't use a lot of charcoal. On the other hand, charcoal fired ECBs use a LOT of fuel because they're (wait for it) so drafty, lose a lot of heat, and need to replace it. This means they circulate dry air, unless it's humidified.
Getting back to WSMs. They are near ideal cookers and I recommend them highly to anyone who's interested in a smoker, portable, or all 'round -- especially if value is a consideration. However, they are practically sui generis when it comes to fire and air management. Many techniques which work well with them don't work at all for other bullets and vice versa.
Hope this helps,
BDL
