<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">So is the theory that "up" will the fat will render and help keep the brisket moist. "Down" will protect the meet from heat and drying out? </div></BLOCKQUOTE>
The former, no, the latter, yes. Keeping the brisket moist is a matter of not overcooking it. Whatever fat that renders from the surface just drips off. It doesn't soak in or anything. Fat down protects the cut from the more direct heat from the bottom. It also avoids the issue of the rub rubbing off due to the grate.
If cooking with water, the grate temp is usually lower. At least it is in mine. I usually cook with nothing in the pan, so it's different in that scenario, but it doesn't matter. My suggestion is to get used to one place - I temp at the lid vent - and go with that. You can make yourself crazy taking temps all over the cooker.