United States Code, 2011 Edition
Title 4 – FLAG AND SEAL, SEAT OF GOVERNMENT, AND THE STATES
CHAPTER 1—THE FLAG [ … ]
§7. Position and manner of display [ … ]
(m) The flag, when flown at half-staff, should be first hoisted to the peak for an instant and then lowered to the half-staff position. The flag should be again raised to the peak before it is lowered for the day. [ … ]
(1) the term “half-staff” means the position of the flag when it is one-half the distance between the top and bottom of the staff; (my italics, for emphasis. DH)
Just as the top of the flag goes all the way to the top of the flagpole, when “half-staffed” the top of the flag should be placed at the “top” of the half-way point on the flag pole. No more, no less. For example, on a 50 ft flag pole, the top of the flag would be placed at the 25 ft mark.