We have an X on Elm Street, we have an X on Tenth Street and we have an X at Love Field.
Is there any map or diagram that accurately shows where the Harper fragment was found?
I don't think that Mr. Harper left a "flag" or anything to show the location. From what he remembered, he found it to the south of where the limousine was at z-312, and about 25 feet away from that position, on the grass. Since the limousine was traveling south west at the time, this would mean the fragment was found ahead and to the left of the limousine.
But we really didn't need for Mr. Harper to have left a "flag". We can see what must be the Harper fragment flying upward and forward in z-313 and z-314. And it ended up on the far side of the road (from Mr. Zapurder's perspective). So it flew upward, forward and to the left. And a shot from Oswald would have come from behind, so this makes sense.
Why did it go so much upward? Why did it go so much to the left? Because a fragment won't generally go directly away from the shooter. They only go generally away from the shooter.
If fragments always did go directly from the shooter, all bones, fragments and blood would have ended up in a narrow circle within the limousine. Anyone very near a shooting victim generally wouldn't get any blood splatter on them. But that is not how it works.
So, a fragment will generally go away from the shooter, but it can deviate a good deal to the left or right. Or up or down. It's pretty random and hard to predict.