Poor airflow from too many bends?

I have one register in my upstairs that has absolutely anemic airflow. It’s one of the farthest from the air handler, enters the upstairs via an unconditioned knee wall attic,… I have one register in my upstairs that has absolutely anemic airflow. It’s one of the farthest from the air handler, enters the upstairs via an unconditioned knee wall attic,…Read MoreGreenBuildingAdvisor