The choice to Foil at 160-170*F is pretty common because at this point the Briskey usually has seen 4-6 hours of smoke, has a decent Bark, flavor wise, and is about to stall anyway. But there is certainly wiggle room. As far as Fat Up, Fat Down, I not convinced it makes a difference. For one thing, by the time we foil the surface of the meat is fully cooked and set. Second, think of Chunks of Chicken being Deep fried. They are surrounded by Fat yet that fat doesn't get absorbed into the meat. The water within the meat becomes Pressurized by the cooking temp and will not allow anything in, especially Fat. The term Greasy Chicken is based on how much Fat is absorbed in the Breading or Coating at low temps, the meat will soak up very little if any unless it is allowed to cool completely in the fat. So, by the time we foil any fat that was going to melt and baste the meat, already has and any remaining surface fat will end up a Puddle in the bottom of the Pan or Foil Pouch. The Bark is softened by the Steam in the Foil. So some further exposure to heat, in the Smoker or on a Grill is needed to firm it up if a Hard Bark is desired...JJ