As with most of the powerlifting as strength exercises, the lats are key. The shoulder press is no different. The lats are some of the biggest muscles in your body. Your ability to use them to pull the bar down will help you decrease stress on your shoulders and rotator cuff muscles. Activating the lats concentrically opn the way down will allow your shoulder to be more useful on pressing the weight up. Think about doing a pull up as your bring that bar down bringing your elbow in front your then driving them back behind you. Also, don’t let the elbows flare out until the bar is passing your head.