This is from the manual:
Jumping Reach reflects how good a player is at reaching the ball in the air. It indicates the highest point an outfield player can reach with his head. It is not necessarily reflective of how tall a player is, but when considering his jumping ability, it makes sense to take into account the player’s height. For example, a player of 200+cm will still possess a high reach even if he is a poor jumper, and a player who measures in at 170cm will struggle to compete at the same height due to the 30cm difference in height between the two.