as we know 14 works but is a little awkward
15 could work with 3 five team pods, 4 games in pod, and play 4 to 5 of the other 10 schools each year.
16 would work with two 8 team sub conferences or 4 pods
18 could work for three 6 team pods or 2 9 team sub conferences
20 again four 5 team pods or two 10 team sub conferences.
21 could work with 7 team pods, 3 of them

the problem becomes that you start to see your other conference buddies less and less on the schedule. We'll be playing ND more often than NC State now.