I think I cracked the code on getting Ancestry DNA circles created. This is from the Ancestry website:
A DNA Circle will form around an ancestor in your family tree if your tree is public and linked to your DNA test, and if two or more of your DNA matches...
1. are DNA matches to you and to each other at a 2nd cousin level or further out
2. have public family trees attached to their DNA tests; and
3. share a common ancestor (according to their trees).
That means there must be 3 or more people that have the same common ancestor in their tree along with the DNA matches to that ancestor. They must have at least three people with DNA profiles in their trees. When I have been successful in getting DNA cousins to add the branch that contains me and my cousins to their tree, and I add those DNA cousins to my tree, a circle is created. Once in a great while, Ancestry has created a circle when 2 people with DNA profiles are in the tree and the third branch is partially complete. It is rare but it has happened.
By the way, even when the circles are created, it has been limited help. It's a nice idea that I hope gets better.