How are the groups-of-100 at each level organized? Is this plan vulnerable to gerrymandering? My (possibly naive) fix is to allow people at each level to join

How are the groups-of-100 at each level organized? Is this plan vulnerable to gerrymandering? My (possibly naive) fix is to allow people at each level to join any group-of-100, as long as the size remains at 100. (For one to join, one has to leave.)