https://www.utexas.edu/student/admissions/research/CAPreport-CAP12.pdf
UT puts out a report on CAP every year. See link above.
“The summer/fall 2012 freshman admissions cycle included 9589 CAP offers; 1881 students returned their CAP contracts. In the fall of 2013, 723 returned to enroll as transfer students at UT Austin. These students (n=723) are referred to as “CAP12” i.e., they were offered CAP in 2012 as freshmen and arrived in Austin in 2013 as transfers.”
About 20 percent of people offered CAP took it. Of those who attempted it, less than 40 percent made it to Austin as sophomores.
It is likely that strong students who were offered CAP chose not to accept it and that keeps the transfer rate relatively low. I believe this was the last class (or two) before they created PACE so these numbers may look different when they start publishing PACE data.