Although the mic may be high enough to clear the frame line, the body of the pole may cut across the corner of the frame. When your arm is vertical with the elbow locked, all you are doing is supporting a couple pounds of weight in a straight line with your body. Also, when your arms start from a true vertical, it is possible to quickly reach in or out with the boom to follow the action. Use your front arm as a fulcrum to support the pole above your body. If the situation permits, grip it towards the natural balance point of the boom.
Microphone Placement Try to position the mic as close to the action as possible.
Depending on the situation and the characteristics of each particular microphone, your mic may be several inches to a few feet overhead of talent. Be aggressive in your mic placement. Ten feet overhead may be very convenient for the camera and lighting crew, but your dialogue will be poor. Professional boom operators often place a strip of white tape on the tip of the windscreen so that the camera operator can readily spot if the mic has dipped into the shot. Better to see the mic in the viewfinder than to wait until it shows up on the big screen.