A circle with a center is different than a group, because there is a spiritual center. The image that most conveys it is a wheel in which all women are sitting around the rim of the wheel and at equal position to one another, with the spoke's energy coming from a center. That centering image is very much the image of what made a house a home, and a building a temple in Greece. The idea was that at the center of any sacred space there was a fire, a hearth and the invisible presence of the goddess Hestia, who is goddess of the hearth. And that's what a centered circle has as an image.
Most circles have some ritual that shifts the energy.
The same thing goes for a circle. It may be music that centers us, that moves us out of social chatter into sacred space. It may be the sound of the bell. It could be that we are silent for a time. It could be that we light the candle in the center.