I'm quite sure that the next round's pool placements are not random. They are based on where you finished in Pool A, B, or C. As I recall, the winner of the group was always paired with either the 3rd or 4th place team from their pool, with the second place team being paired with the remaining team from their pool. Then 3 pairs from each of the original 3 pools, form a new pool so that each of the new pools will have 3 teams that finished in the top 2 from their previous pool, and have at least one team that finished first in their previous pool. I hope this makes some sense.