A “flat” organization generally operates as a collective in that each and every member tends to be involved in every decision and limits positions of authority or power. Further decisions are made using consensus.
In that sense, Sociocracy is not a flat organization as it uses a hierarchy with key positions such as Delegate, Circle Leader, Facilitator, etc.
However, a flat organization could use sociocracy for its governance model by simply limiting the time that any one person can be in a role of leadership or authority.
For more information, check out our handbook Many Voices One Song chapter 1