Every player gets “measured” during spring training and their strike zone is stored. If a player is not in ML spring training, they can be measured when they get called up. This also accounts for exaggerated crouches etc. And if you watch on TV, the dot is where it crosses the plate, not where the catcher catches it. Oftentimes, the ball will almost hit the ground on a curve ball but will touch the bottom of the zone. The strike zone is based on where the player is when they are prepared to swing. You can effect your strike zone by how you crouch etc...it is not consistent from pitch to pitch, by batter, and not directly based on your height.