In case moving the larger image outside of the element with "overflow:hidden" and position, is not an options for you, you will have to use another approach to scroll the images with a RadSlider - an approach that would not use position, top and left properties.
You can, for example, change the marginLeft of the inner DIV element, instead of the left property. In this case you can use elements without position and the only positioned elements would be the larger images. In this case, you will not have problems showing those larger images outside of the scrollable container. I have attached a simple page demonstrating this approach.
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