Constant tension that stretches and blasts the long head.
Pin your elbows in place, let only your forearms swing.
Facing away from the low pulley with the rope behind your head, your arms are overhead where the triceps' long head is stretched to its limit, and the cable keeps pulling into that stretch on every rep. Extending to lockout while the elbows stay pinned makes the long head, the biggest chunk of your upper arm, do all the travelling. Arm size lives in ranges like this one.
The long head of the triceps crosses the shoulder, so it only reaches a full stretch when your arm is raised. Overhead extensions load that stretched position directly, which pushdowns with your arms at your sides can never do.
Letting the elbows drift wide and forward as fatigue hits, which shortens the range and turns it into a strange press. Pin the elbows beside your head and treat them as a hinge, only the forearms move.
Take a staggered stance with a slight forward lean, which opens up the overhead position, and start lighter, this movement punishes heavy egos. If it still pinches, build shoulder mobility and lean on pushdown variations meanwhile.
