If the Pixie App is asking you to walk in an L-Shape, it means that the Panorama scan was not able to locate your misplaced item. Pixie App then defaults to this alternate search method.
Pixie uses triangulation to locate the position of your Pixified items. In order to do this, the application needs to take several distance readings from different locations. Walking in a L-shape takes several distance readings and allows the app to calibrate not only the distance but also direction.