The rest of Rift and Touch holders have the two sensors that come with the purchase.
Oculus it has updated Rift user hardware reports to include the number of sensors used, as published by UploadVR. Currently only the 20% of users of Rift they chose to separately purchase one or more of the sensors to ensure better coverage of their room and follow the guidelines Oculus published last year.
Oculus recommends placing in front of the two sensors that come standard with the Rift + Touch package, as if it were a system of 2 stereo speakers, and a third behind at least to achieve better coverage of both the viewfinder and the motion controllers in 360º configurations. However, most users use a room space configuration that encompasses the 2×2, 5 meters (2 to 2.5 wide and 1.5 to 2 deep), so it is also possible to achieve 360º coverage by placing a sensor in each corner.
In general, most games have a locomotion system that does not require us to move physically at 1: 1 scale, being possible to enjoy with configurations of two sensors in 180º.