Those bottom 4 teams are expected to lose. In that case the 3/4 teams would be playing the higher remaining seeds (5/6) and the 1/2 teams would be playing the 7/8 teams. But when the bottom four teams win then 3/4 gets the benefit.
In the NHL and NFL teams are reseeded after each round. In that case the lowest remaining seed always has to play the highest remaining seed.