Isolate one side of the chest for a killer squeeze.
Pull across the midline for the full chest squeeze and keep that elbow bend fixed.
Sweeping one handle from a high pulley down and across your body takes a single pec through its full job, driving the arm across the midline where presses stop short. The front delt assists the arc, but the squeeze as your hand passes toward the opposite hip is all chest. It earns its place because crossing the midline one arm at a time gives a longer range and a harder peak contraction than any two-handed fly allows.
One arm can travel further across your body without the other handle in the way, and each pec has to work alone. It is the fix when one side of your chest lags or dominates.
Past your midline toward the opposite hip. Stopping at your centre line leaves the hardest and most productive part of the contraction on the table.
Softly bent and locked at that angle for the whole rep. If the bend opens and closes you are pressing, not flying, and the chest loses the isolation.
