It is arbitrary. When you think about it a moment, there is about as much of relationship between enrollment ratios and participation ratios as there is the between the Dow Jones average and the number of tuba players in the band. The courts have not ruled that it is not discrimination against males or a violation of Title IX to try to achieve proportionality by eliminating males. In a recent case in Bakersfield, California the Federal District court ruled that it was a violation of Title IX to eliminate males to try to achieve a quota. Quotas equal discrimination by their very nature.
Proportionality increases female participation.
Proportionality is used only to eliminate males. There is not one case that can be documented where proportionality was used to increase female participation. There are two other rules under Title IX that require schools to continuously increase female participation or accommodate all of the athletic interests of all of the females on campus. These two rules are used only to increase female participation. Schools are not limited to proportionality to avoid charges of discrimination.