Joe Pak wrote:

"I understand the thinking behind the baffle and the bricks, but what does
lowering the chimney to grate level do?"

In my opinion, nothing good. Unless you like creosote, bitterness, and
oversmoked food.

I used to have my chimney down to grate level on my smoker, but pulled the
extension off. I think improving the draft through the pit helps improve
the end result with food flavor. In my beginning days, I smoked the heck
out of everything, thinking that it made for good BBQ. Now, I've discovered
that good BBQ means a proper balance of smoke flavor to meat/spice flavor.
You'll find in many championships, the number one or two complaint judges
have with BBQ is "oversmoked flavor." Pulling the chimney down to grate
level does two things: Holds the smoke in the chamber longer at a lower
level, and helps hold heat. If you're bricking up your pit bottom, the heat
retention problem is solved.

Just my two cents... (worth four cents in this housing market)