OP sorry no one really understood your observation and question. With the lock-on setting the distance, the game has the third number to work with, and this number has an intuitive reference for the player: the enemy's ship distance. Think of the green line in the last image, that's basically the line at which the center of your screen is pointing your shots to go with only 2 numbers the game has to figure out at which point of that line you actually want your shots to pass through in its curved trajectory. Without the lock-on setting the distance, the game would have only 2 numbers to use for the aim, lacking the third one. The lock-on is meant to let you have a good aim in a 2D perspective, despite having to hit a target in a 3D environment. That allows for a more precise vertical aim on the ship. The lock mechanism simply ensures the aiming dispersion ellipsoid is fixed at the target's distance, instead of the distance of the point at the center of your screen. SubOctavian mentioned it in old dispersion commentary.

Where to aim world of warships