Thank you for your reply.
I use same base stations. The version is 1.0.
VIVE Pro always white out if I occlude one sensor with my finger. But, VIVE does not. "back-facing" event occurs when the sensor is occluded for a long time, but not for a short time. However, white out occurs immediately. This is fatal for shooting game.
I hope that this will be improved with a firmware update.