Why does the customized video slideshow preview looks different than the actual tour

The preview is only an approximation of what you'll see since the player's aspect ratio cannot be predicted in advance. The way the image looks in the player depends on not only the custom rectangle you've set up, but also the aspect ratio of the image and the aspect ratio of the player. It also depends on our "snap to fill" setting which will zoom the image by about 30% to avoid letterboxing of the image.

The bottom line is that the preview is just an approximation, so don't expect it to or depend on it to look exactly the same in the player.