The traditional and recommended camera layout places one camera at the 6 or 11 position, with the remaining two cameras mounted 120° apart.
It is also possible to mount one camera at the 20 position.*
Mounting a camera at the 3 position is strongly discouraged, as bounce-outs may strike and damage the camera or the camera arm.
* In general, you are free to choose the camera positions as long as the three cameras are spaced 120° apart. However, depending on the chosen arrangement, slight differences in detection accuracy may occur.