Shoulders Up, Chin Up, Alert, Like A Gazelle
Taller is better because most of the high jump approach should be run in a tall position!
Some jumpers will start out leaning forward a bit and some will start out running tall, either is ok so long as the jumper is running tall by the middle of the straightaway.
Running tall continues through the straightaway and around the curve through takeoff. In fact, a common term used to define takeoff is called “running into the air”.
“Running into the air” means the jumper is still tall and poised at takeoff. There’s no forward leans, breaks in the block angles, or big center-of-mass drops which destroy rhythm and move energy away from upward delivery.
Here’s a video of Jaimi Nieto talking about running into the air (running off the ground).
That’s why the high jump approach should be run in a tall position, to promote correct blocking angles and upward momentum delivery in a smooth and effective manner.