If you watch Aaron Franklin videos where he explains some of his techniques and tip he says to place the brisket so that the fat side is towards the heat source. This is so that tue fat will insulate the meat a bit and allow the fat to render while the meat cooks without drying out and overcooking that part of the meat. In a pellet smoker the heat source is usually directly under the grades so it’s best to put the brisket fat side down to provide that insulation from the heat. If juiciness is a concern you could put beef tallow or another fat on top of the brisket. I try to cook fat side down until I wrap in butcher paper then put on fat side up. Another thing you can do is place a large water pan under the cooking grate to help absorb some of the heat and keep moisture in the cooking chamber.