Изменение логики масштабирования изображения

$('.preview').each(function() {
  var lens, cx, cy, img, result;
  img = $(this).find('img.image')[0];
  result = document.getElementById('result');
  /*create lens:*/
  lens = document.createElement("div");
  lens.setAttribute("class", "img-zoom-lens");
  /*insert lens:*/
  img.parentElement.insertBefore(lens, img);
  /*calculate the ratio between result DIV and lens:*/
  cx = result.offsetWidth / lens.offsetWidth;
  cy = result.offsetHeight / lens.offsetHeight;
  /*set background properties for the result DIV:*/
  
  /*execute a function when someone moves the cursor over the image, or the lens:*/
  $(lens).on('mousemove touchmove', moveLens);
  $(img).on('mousemove touchmove', moveLens);

  function getCursorPos(e) {
    var a, x = 0,
      y = 0;
    e = e || window.event;
    /*get the x and y positions of the image:*/
    a = img.getBoundingClientRect();
    /*calculate the cursor's x and y coordinates, relative to the image:*/
    x = e.pageX - a.left;
    y = e.pageY - a.top;
    /*consider any page scrolling:*/
    x = x - window.pageXOffset;
    y = y - window.pageYOffset;
    return {
      x: x,
      y: y
    };
  }

  function moveLens(e) {
    var pos, x, y;
    result.style.backgroundImage = "url('" + img.src + "')";
      result.style.backgroundSize = (img.width * cx) + "px " + (img.height * cy) + "px";

    /*prevent any other actions that may occur when moving over the image:*/
    e.preventDefault();
    /*get the cursor's x and y positions:*/
    pos = getCursorPos(e);
    /*calculate the position of the lens:*/
    x = pos.x - (lens.offsetWidth / 2);
    y = pos.y - (lens.offsetHeight / 2);
    /*prevent the lens from being positioned outside the image:*/
    if (x > img.width - lens.offsetWidth) {
      x = img.width - lens.offsetWidth;
    }
    if (x < 0) {
      x = 0;
    }
    if (y > img.height - lens.offsetHeight) {
      y = img.height - lens.offsetHeight;
    }
    if (y < 0) {
      y = 0;
    }
    /*set the position of the lens:*/
    lens.style.left = x + "px";
    lens.style.top = y + "px";
    /*display what the lens "sees":*/
    result.style.backgroundPosition = "-" + (x * cx) + "px -" + (y * cy) + "px";
    console.info(result);
  }

})

* {
  box-sizing: border-box;
}

.img-zoom-container {
  
  width: 100%
}

.preview {
  display: inline-block;
  margin: 0 10px;
  position: relative;
}

.img-zoom-lens {
  position: absolute;
  border: 1px solid #d4d4d4;
  /*set the size of the lens:*/
  width: 40px;
  height: 40px;
}

.img-zoom-result {
  border: 1px solid #d4d4d4;
  /*set the size of the result div:*/
  width: 300px;
  height: 300px;
}

<script src = "https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script>
</script>

<h1>Image Zoom</h1>
<p>Mouse over the image:</p>
<div class = "img-zoom-container">
  <div class = "preview"><img class = "image" src = "https://www.w3schools.com/howto/img_girl.jpg" width = "200" height = "200"></div>
  <div class = "preview"><img class = "image" src = "https://placeimg.com/640/480/animals" width = "200" height = "200"></div>
  <div class = "preview"><img class = "image" src = "https://placeimg.com/640/480/arch" width = "200" height = "200"></div>

</div>

<div class = "img-zoom-result" id = "result"></div>