The Section C11 percentages are on a 4.0 scale.
https://oir.harvard.edu/files/huoir/files/harvard_cds_2018-19.pdf
From that CDS:
“C11 Percentage of all enrolled, degree-seeking, first-time, first-year (freshman) students who had high school grade-point averages within each of the following ranges (using 4.0 scale). Report information only for those students from whom you collected high school GPA”
Unclear on what basis the C12 “mean” number was determined, but it clearly wasn’t on a 4.0 scale.