A few problems with the way it's being used here in the video.. The metal screens are designed to fit certain bowls, I find it works best with a medium sized Mya-saray bowl. It's also better to use Three Kings brand large coals, since they fit perfectly on the tin, and maximize airflow. Having the metal screen fit the bowl properly also maximizes airflow. Having a gap between the tin and the bowl hurts airflow, having exposed holes hurts airflow. Be sure to pack your bowls a little lower than normal, since the metal screen goes down below the top of the bowl a little bit. Packing it too high will just char your shiisha real quick. I personally use a metal screen when I'm not using a phunnel, just so I don't have to dick around with foil and it works quite well for me. When I pull the top off after the bowl is cashed, I usually find a small amount of ash. I think you got more ash because of the coals you're using. A large sized coal will deteriorate more slowly than two small sized coals, and the small coals will have to be placed at such an angle that they deteriorate on one side first, requiring a lot of movement during the session. With the set up I use (described above,) I get more smoke, better flavor, and less ash than any other set up I've tried besides the phunnel.