The technical specifications for the range of the Structure Sensor is 3.5 meters but that is the range that it can “see” and not the actual scanning size, which is what you are looking for.
The Bridge Engine, as well as all of the Structure Sensor Applications, limits the size that can be scanned, not due to the limitations of the Structure Sensor, but due to the hardware limitation on the iOS devices being used with the Structure Sensor. The largest limiting factor for the size of your scan is the memory (RAM, not storage) on your iOS device, which is typically 1, 2, or 4 GB. We, thusly, limit the size of the area that can be scanned to make sure that all supported iOS devices can handle the scanning size.
Also, the Structure Sensor is not suited to work outdoors in strong sunlight, as the amount of ambient infrared light interferes with its operation. For use outside, the Structure Sensor would work best from dusk until dawn or on an overcast day, when sunlight is at a minimum.