The back judge on this play is lined up at the end line and the foul is at or near the 20. How many of us can throw a flag 30 yards and have it land exactly where we want it to? I know I can't. So you're going to have to move it at least a little in these situations. The down box may be a good reference on this play (assuming he saw the flag and hasn't moved), but what if the foul is not at the LOS?