To clarify, the original group was going to have 6 people and the center limit was to be from 12 1/2"- 18 1/2". Each round would be from 3 1/2" - 6 1/2", dividable by 3's.
Then as more people asked if they could join, we started making groups of 5 each, with the center size from
12 1/2" - 24 1/2"with each round being 3 1/2"- 9 1/2" dividable by 3's.
The size of each round is up to the person adding that round. The person adding the round looks at the top and adds what that person feels that the center needs.