Does "lower position" mean lower or higher ranking number?
Sorry but you might have been confused because of the mistake in the rule: letters A and B were swaped. The mistake has already been corrected.
From the quarterfinals, Player B at the lower position (in Ranking Table of given tournament) to Player A, can use the rule:
"I post pick: Ccccc over Ddddd
if Player A picks the same, reverse my pick to Ddddd over Ccccc".
So the "lower position" means lower ranking number (which also is a smaller number of points).