If you have any sort of shoulder pain, primarily impingement issues, when performing any sort of overhead pressing or reaching, it is most likely an issue with your scapulothoracic alignment (posture of your shoulder blades in relation to your back), than it is a shoulder joint problem. Even more specifically it is most often an issue with thoracic spine extension (straightening of the upper back).
For example, take a person with the all-to-typical forward-rounded shoulders and head posture, which can be caused by too much sitting with the arms forward (i.e. sitting at the computer the majority of the day) or starting each and every workout with the damn bench press (there are other lifts) or any other activity that has the shoulders, arms, and head out in front of the body for long periods. A rounded forward thoracic posture (kyphotic posture) will force the scapula (shoulder blades) into abduction and an anterior tilt. Basically pushing the scapula out and over the humerus. Now when a person tries to press or reach overhead, the scapula, specifically the acromion process and the humerus run into each other, causing impingement. Most times the infraspinatous is the muscle being impinged. Regardless, most times this issue can be resolved with work on mobilizing the thoracic spine into extension.
To work on thoracic extension, sit in a chair in which the back rest comes up to middle of the back. Place your hands on your head with your elbows pointing to the ceiling. Using the top of the back rest as the fulcrum, bend backwards over the chair, pushing your chin back into your neck and chest up. This will help mobilize your thoracic spine into extension and adduct and depress your shoulder blades. This clears the scapula back and down to free up the humeral head to move properly. Do 10 reps every hour to 2 hours, especially on the days which you have to sit a lot.