Hi,
If you have the right components (good IR pen/original Wiimote) and placed the Wiimote at the optimum position, screen sizes of about 2m and above in diagonal should work fine.
For very large screens, you will need to place the Wiimote as close as possible to the screen by ensuring high tracking utilization. If tracking is bad even with the right components, you can use two Wiimotes to improve the tracking utilization.
From my experience, screens with the size of an actual whiteboard height works well with little need for ensuring high tracking utilization. However, with very large screens with the size of almost the entire wall, you will need to take time and effort to get good tracking.
Regards,
Boon Jin