In my VERY limited experience, when the meat is closer to being done, I close the vent halfway to increase the internal cabinet temp. It seems after 10 hours in the OBS, I get that plunge from 225-240 to 170-180 for at least 2 hours. It got so bad the other day that I took my brisket out and used my oven to finish it off. The cabinet went from the 170-180 back to 225 in no time. It's happened to me twice the exact same way, coincidence, probably. The guys on here know their stuff, just pick and choose what works for you and the food you're cooking.