2012 championship game: 18,818; 2016 championship game: 19,358 (3rd highest all-time, trails 2007 championship by less than 100. Hard to see 2010 in Ford Field ever being beat with 37k)
I read the semi-finals were slightly higher in 2012, but cannot find the article.
2012 participants were BC, Minnesota, Ferris St., and Union. So two big schools, and two small schools.