This was written by Don Slaught for the NFCA published in May 09 this is just part of the article.....
"Note that it is your mental approach that should change or adjust from pitch to pitch, not your mechanics. We should adjust mentally after each pitch to what we just saw and felt, (we say see it, feel it and fix it) but we do not want to start messing with our computer by physically changing our mechanics. Remember any changes to your stance, length of stride, choking up, or moving in the box will affect not only your mechanics but also your data base. Changing or adding variables to the equation is not the answer when you are in a pressure situation. If you move a couple of inches closer to the plate on any particular pitch, your data base that you have built for years will also move a couple inches closer to the plate. The same goes for moving forward or backwards in the box: you've seen thousands of pitches from one spot in the box, so why change now? This doesn't even take into consideration that the catcher can see these changes. (also whoever is calling pitches for the catcher) These physical adjustments are very difficult to make and really take a lot of training to be successful. If a physical adjustment feels better, then it should be done all the time. A perfect example is Barry Bonds; he began choking up with two strikes and had great success and decided to do it for the next 17 years."
We say we are creating our swing DNA and Don uses computer or data base however it is what the hitter sees as to where to hit the ball every time they see a pitch. I call it a window of opportunity and have defined it as being about 12.5 inches front to back on the plate. We use the back corner of home plate to measure off from and the back of the window from there is about the width of a shoe forward and 12.5 inches from there or about the length of a shoe toe to heel plus 2 to 3 inches seems to work for most hitters. IF we decide to move forward in the box we teach them to take the mental picture of the window with them so they have a reference and we also do the Barry Bonds drill so we practice doing this. Most coaches who order a hitter to move up or back in the box have not practiced it so they are changing the hitters swing DNA without consideration of the hitters ability to perform it. We also teach our hitters to call balls and strikes as THEY must determine what they can hit not the umpire. We have demonstrated we can hit a ball that is 11 inches off the plate by the way we measure off from the plate however we only want them to hit it 5 to 8 inches off the plate and adjust mentally in the count to what we think we can hit. I do not use the phrase with two strikes protect the plate...hit what you feel is hittable when you want to hit it!
Some of our kids have hit home runs, tripples and doubles off intentional walks as the catcher never set up far enough off the plate and the coach knows them well enough to give them the green light to determine what they hit.