Hi @creatingworlds, the Tobii Eye Tracker 5 is setup initially by defining the screen size and parameters of the connected monitor. Any gaze data that lies outside this established boundary is necessarily reported as NULL as we cannot guarantee any accuracy outside the screen boundaries. In order to cover a larger area and retain Tobii data, you would need to use a larger screen size or at least use a large screen initially and perform a calibration and then replace with a smaller monitor which lies upon an identical plane.
You could also look at one of the free projects that calculate eye tracking based on webcam footage that could take over when the user gaze lies outside the screen boundaries?