Smoking Brisket

Yesterday I was smoking a 11.5lb prime brisket. it was a very windy day but averaged about 250 degrees in the cooking chamber with occasional swings to 270. I placed the brisket in the middle of the cooking chamber with the point towards the fire box and maverick temp probe in the thickest portion of meat. Approx 5 hours in I reached a temperature of 160, at which point I wrapped the brisket in butcher paper and continued smoking until temp reached 203. I took the brisket off and placed in warmed cooler . Total time in smoker 13 hours. Hold time in cooler 90 minutes.
The brisket had a beautiful smoke ring, the point meat was perfect, however the flat seemed dryer than normal. I'm not sure why and haven't experienced this before with previous smokers I have had over the years. Also did baby backs and they were perfect. Any suggestions on what I may have done wrong with the brisket or suggestions on what to do differently new time? Thanks so much.
The brisket had a beautiful smoke ring, the point meat was perfect, however the flat seemed dryer than normal. I'm not sure why and haven't experienced this before with previous smokers I have had over the years. Also did baby backs and they were perfect. Any suggestions on what I may have done wrong with the brisket or suggestions on what to do differently new time? Thanks so much.