Cables from both sides crush your chest right at the midline.
Keep that elbow bend locked and lead with your hands, cross slightly at the front for extra squeeze.
With both pulleys set at chest height, the line of pull runs straight across the middle of your chest, biasing the mid pec fibres as you sweep the handles together. Unlike a dumbbell fly, the cables keep pulling sideways at the point your hands meet, so the squeeze at the midline is fully loaded instead of being a dead spot. Your front delts assist through the arc, and the deep stretch at the open position is where a lot of the growth stimulus lives.
The pulley height changes which part of the chest gets the bias. Mid height pulls straight across for the middle of the pec, high pulleys sweep downward for the lower chest, and low pulleys sweep upward for the upper chest.
A slight crossover adds range at the point of peak contraction, which is the whole reason to use cables. Alternate which hand goes on top set to set so both sides get the extra squeeze.
Less than your ego wants. If your elbows are bending and straightening during the rep it has become a press, keep the elbow angle fixed and let the chest sweep the arc.
