Fuel matters. Burning wood with a visible flame creates more NOx than charcoal and glowing coals will. So, to maximize the smoke ring, use a stick burner and try to keep the temp low for as long as you can before the meat hits the magic 130-140 where the ring formation is halted. If you don't have a stick burner, try more wood chunks. Keeping the surface moist in this phase is supposed to help capture the smoke.
Bark seems to do better with higher temps and less moisture. After the ring is no longer forming because you hit 140, up the heat and airflow. Perhaps start at 200 for a few hours and then bump to 275-300. You can add spice but try basting in oil only and not water if at all at this point. I don't think you need a thick layer of spices to get what I consider a good bark, but if that is what you want and you think it is blocking smoke penetration after further testing, try adding it mid cook after staring the cook with a simpler salt based rub.