Why VIVE HMD higher than the floor

I put a playerstart in the level,the VIVE hmd always higher than the floor.It seems everything has add a offset.

If i put the middle of playerstart a little higher(like 0,0,1) than the floor,just as the official web says,it turns to be “bad size”.When i run vive,the hmd is on the correct position now but I can not use the motion controllers this time.

I’m confused for many days.Please help!!
Thank you very much.