I kind of waited until this thread had worked its way out to offer my thoughts. Its basically the same as I have posted over the years, but it has worked for me...
My zone is just what happens when I am behind the plate attempting to judge a 3 dimensional strike zone that changes based on the batters height.
If you can imagine an invisible floating column, 17 and a half inches wide that extends from a horizontal line at the midpoint between the top of the shoulders and at the lower level is the hollow beneath the knee cap. The zone is determined by from each batters stance as the batter is prepared to swing at a pitched ball....the strike zone changes for a 5'6" batter to a 6' batter......
All of this adds to each umpire having slightly their own zone....even as we all try to adhere to the rule book definition.
It is just the reality of doing the job. I am known as an inside and low ball umpire. I know this from video tape of my cage work at umpire clinics. I am more apt to call a ball a strike inside and low than I am at the outside and high side of the zone. Its just my reality...maybe its because I am short that I see that lower ball as a strike. Dont know, not sure what I can do as a human to improve on that.
I try and keep as consistent a zone as possible to avoid problems, but it is what it is.
Given that, in games with umpires of my experience, you will get different zones...much of it based on such things as the umpires height, his stance and the quality of the catchers.....
I believe that most trained umpires call zone with the rule book in mind and to the best of their ability..... Going back on my training, I can tell you based on video proof, that I call the borderline pitch inside and low a strike, but the outside and up pitch a ball.....now that is defining "my zone" over the strict rule book zone....
Its a condition of my height, my stance, my experience and probably a hundred other factors.......I keep working to refine my zone, but truth be told, I probably wont ever get it book rule perfect.....
I hesitate to offer this statement since usually this is the childs way out, but I will offer that it isnt as easy as it seems.....But I will guarantee you that I will keep trying to get better.......
Despite all our efforts, I feel there will always be some variance.......but I will try to get better......if at any time I feel I am doing "good enough" and fail to work on refining my game......I will call it a career.......