It's definitely the size and resolution of your screen. If I read the specs correctly, it's 11.6 at 1920 x 1080.
While at the Start Screen, try going to the Charms bar, click on the gear and see if you have an option for 'Tiles'. If so, click on it and see if it has the option, 'Show more tiles on the Start Screen'. If so turn it on. You will get more rows on your Start Screen. Hopefully that will trigger the Desktop Tile to allow the larger resize option.