I am thinking if you add 40 lit coals to the unlit coals in the basket, how much time are you giving the unlit briqs to catch before you hang your meat and put on the lid?
None, per Amber's direction:
"Hi Ed,
Thank you for the email, when using a chimney you will fill your charcoal basket full remove 1/4 of them (40 briquets) and light. These will burn for either 12-15 minute minutes if you are 2000 ft or below or 20 minutes for all elevations.
Once you have allowed this time pour them on top of the unlit coals as you did put the lid on and cook immediately. Sometimes for whatever reason cookers can stall, if this happens you can always crack the lid about 1/4" for 20 minutes or so to stoke the coals and get the heat going. Feel free to call should you have further questions our direct line is on every cooker."
Given the posts here explaining methods and describing results, and my results after following this advice, this is clearly not accurate. I did try cracking the lid on two of the cooks, and although the temp came up a bit, it never got to the described range and the cooker cooled again fairly soon after closing properly.