Someone else just recently posted that there is a different “formula” for smaller schools in TX: http://talk.collegeconfidential.com/university-texas-austin/2101844-automatic-admission-for-students-from-small-school-for-ut-austin.html
When universities publish their incoming class profile they will often provide a combination of data - rank, GPA, and test scores.
The adcoms know there is wide variability school to school.