Take any existing campaign that is targeted to both desktop and tablets, change it to just desktops, duplicate the campaign and target the new campaign to just tablets. This will allow you more control to bid for higher positions on tablets that you might not want to do on desktop. It will also allow for easier reporting for tablet performance.
Another reason to have device-only targeted campaigns – in this case for tablet targeting. I’ve seen this happen enough in my own accounts that I’ll bet the same is true with everyone: ads that are above the fold on tablets have a click-through-rate up to 10x higher than below the fold.