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I've smoked two 16# whole packers both times without foil. The first time I cooked to temperature (195 degrees) and the flat came out chewy - I thought I overcooked it. My wife and son didn't like it. I did a lot of research for the second one and was going to foil it at around 165 but during the cook I was doing some more research and realized that I had in fact undercooked the first brisket. So I didn't foil after all but instead cooked to tenderness - until my thermopen slid in without resistance. This second brisket was perfect. There were 2 other differences between the first and second cooks: On the second I filled my drip pan with water for the entire cook and basted brisket with drippings every so often after it hit 165.
So my vote would be to not foil and to make sure you cook to tenderness and not temperature. Note that my Maverick reads 7 degrees high so digital thermometer differences can also affect cooks - all the more reason to check resistance with a fork/probe/toothpick.