What seems to have helped my OHS flexibility issues, and they are many, is to hold the bottom position(warmup loading only) and just feel whats tight and try and work it out. I'll carefully shift my weight onto one foot, emphasize driving the heel into the floor then shift to the other foot. Stay in the middle and really flair out the knees to stretch the hips and even gently bounce a little, consciously activate lumbar and abdominals. All the while working for improved overhead position(retracting/elevating scapulas, 'pulling the bar apart' while pushing it away, getting head forward etc.)
Better yet, read Coach Everett's book.