From what I have gathered from the tests that were conducted with this band heater type of vaporizer tended to indicate that the warm vapor has to displace the air within the hive and the air and vapor moved more easily in the direction of the leaking air. Obviously lifting the cover will allow air to move in that direction but entails more movements in the treatment.  If the vapor is injected at a higher level the vapor will more easily penetrate the upper area before eventually exiting from whatever air leaks there are in the system mostly downwards.  As far as the cluster is concerned in tests carried out in an observation hive the bees immediately break cluster and run around the frames and hive insides as soon as the vapor is injected.  This may not be the case in a full hive as I have not been able to observe such a hive but believe the behavior of the bees would remain the same.  I have also found that the vapor exiting this device cools rapidly so that at a distance of 1" to 2" from the vapor outlet the vapor has cooled to such an extent that you may take the full 2 gram charge on your forearm where much of the 2 grams will adhere to the hair on your arm.  I did not try to measure the temperature of the vapor but felt no discomfort on the arm.  Most of these tests were carried out in the early winter of 2016 and on a cool still morning the vapor would definitely rise and there was no doubt that the vapor consisted of fine particle crystals as they could be seen glinting in the sunlight as the vapor rose toward the morning sun.  These are the observations I made at the time and the conclusions I reached for what they are worth.
John

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