Here is an interesting item about UNC:
“In March of 1986, the UNC Board of Governors adopted policy 700.1.3, which capped out-of-state enrollment at no more than 18 percent of total enrollment.”
http://mediahub.unc.edu/university-ratio-unc-systems-82-18-split/
There is graph in the article that compares nonresident enrollment at several of “Carolina’s public peer institutions.”