Reverse cable X over for rear delts
Reverse cable X over are great for hitting rear delts as you can actually go beyond 90 degrees shoulder horizontal flexion at the shoulder. The height i have here means that you are less likely to let rhomboids overtake in the movement.
Keep the arms a fixed bend, and only move the shoulder joint. Pause at the bottom to feel the rear delts engage more.
This exercise is a great way to start of a shoulder workout and even start off a back workout as it will start synovial fluid being secreted in the shoulder joint capsule.