Tilt the bench to keep tension on your triceps the whole rep.
Keep your upper arms fixed at that backward angle, don't let them drift toward vertical.
Setting the bench to an incline shifts your upper arms behind your head, which drops the triceps' long head into a deeper stretch than a flat skull crusher can reach. Because the bar hangs behind you rather than over your face, tension stays on the triceps at the top instead of vanishing at lockout. It earns its place as the stretch-focused triceps builder in a barbell setup, hitting the mass of the arm that only loaded lengthening really grows.
Arm angle. The incline tips your upper arms back overhead, deepening the stretch on the long head and removing the dead spot at the top where flat skull crushers briefly unload. More stretch, more constant tension.
Try an EZ-bar for a friendlier wrist and elbow angle, drop the weight, and slow the lowering phase. Letting the bar drift behind your head rather than to your forehead also tends to spare the elbows. If pain persists, swap the movement for a while.
No need. Extend until the triceps are fully squeezing, but slamming into an aggressive lockout mostly stresses the elbow joint. Keep the turnaround smooth and save the aggression for the stretch position.
