Which version of ROS do you run on these box? I had a 14km link that had similar problems; good signal, no noise, but low CCQ. I updated the ROS version from 2.9.7 to 2.9.23 at each end and saw the CCQ pass from 20-30 to 60-70 and the throughput pass from 2-4mbps to 15mbps. I did not change anything...