Also, some schools use programs like the Posse Program to help source disadvantaged URMs, so have that as a resource to help boost numbers. So, you may see these less interested in giving URMs applying outside such programs a bump relative to some other schools. For example, Middlebury has 3 posses a year for a total of 30 students. That gives them a good start to getting their target URM percentage.
https://www.possefoundation.org/our-university-partners/participating-schools