As an example, in semifinals phase, group 1 will be assigned players ranked 1st,3st,5th,7th,10th,12th,14th, and 16th. And group 2 will be assigned players 2nd,4th,6th,8th,9th,11th,13th, and 15th.
That would be unnecessarily unfair to the people in group 1, which would have better players and thus be harder to win. It would be better to alternate like this: 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1. This can be generalized to n groups by placing the first n players in groups 1 to n in that order, then placing the next n players in groups n to 1 in that order, and keep alternating between going from 1 to n and from n to 1 until the groups are full, e.g. for n = 4: 1, 2, 3, 4, 4, 3, 2, 1, 1, 2, 3, 4, 4, 3, 2, 1, ...