When we zoom on the map, sever generates new map for shown. We can observe in .tmp folder. Although, img.x, img.y of step 1.3 and 1.6 is 240, 260 too, but attributes is different. Moreover, imgext changes. Summing it up, img.x, img.y of step 1.3 and 1.6 is different position on the map because zoom get new image that get new imgext. New Imgext of new image is calculated new img.x and img.y.
When zoom in on the map, the server will create a new map to display. The position of the selection and location of the map to change because the zoom. The map was zoom will cover a smaller areas, but clear up and the img.ext will be recalculate.