Next to the constitutionally required meetings of Tactical + Governance you can have any kind of other meetings that you find will move the organization forward (or meetings just for fun). Is there e.g. a certain value chain across circles in the org, then you could e.g. come up with a special meeting to sync the different roles or just call in a focus meeting with roles from different circles if it's necessary.
What is the detailed tension behind the need that the 3 circles need to talk?