Generally, students get more expensive to the college as they move up in class level (large common introductory courses cost less than small specialized upper level courses), so frosh at most four year colleges overpay relative to seniors who pay the same (flat or per credit) tuition. Flat tuition over all four years slightly increases this inequity.
However, it is likely that students and parents prefer consistency and predictability of tuition rates over having them start low but increase significantly (much more than 4% per year) with class level.
Other tuition inequities can involve choice of courses and major, since some courses require more expensive faculty and/or more expensive facilities.