See also:

When there is an upward slope at the back
1) 3 feet (1 m) The distance on the screen looks farther than the actual distance. ...

For U.S.A.
The following information has been compiled according to Code of Federal Regulations “Title 49, Part 575”. ...

Rear center seating position
The head restraint is not intended to be used at the lowest position. Before sitting on the seat, raise the head restraint to an appropriate position depending on your sitting height. ...