Handling this in set analysis is very difficult what I can suggest is arrive a flag in script and then use set analysis to exclude the duplicates, try like below
LOAD *,Ord(Pos1) + Ord(Pos2) as Value;
LOAD * Inline [
If(Peek(Value) <> Value, 0, 1) AS IsDuplicate
ORDER BY Value;
DROP TABLE Temp;
Now in chart try below expressions
Hope this helps you.