By bringing the fullback inside it leaves the whole wide area open for Wallace/Whittaker to attack, and both of these players have a good cross on them. It gives us the opportunity to both use Jelavic's physicality in the box by playing in our fullbacks, and playing it into Jelavic/Naismith/Lafferty's feet by cutting inside. I agree with the OP that it is a good tactic but whether it will work, time will tell.