The circle shape makes you feel engaged and able to converse with everyone so it feels cohesive. It's also pretty obvious you were arranged in that shape to emphasis a group conversation activity is taking place.
Kind of the opposite as when you get seated at a restaurant in a long rectangle table. You immediately know it will be difficult to talk to the whole table and will have multiple conversations taking place. If you're at one end, you'll likely only talk to 3-4 people. If you're at the center, you might talk to 3-4 to the left and right but they'll be different conversations. Not that this is a strict law of table talk, just kind of what usually takes place. Sometimes there's something that comes up that gets everyone's attention and the whole table is shouting. An even more extreme example, is a bar top seating, where you are just a line facing the same direction. You might only talk to your neighbors and possibly their neighbor but it's not great at facilitating larger group discussion.
If you ever go to a banquet or wedding where they have round tables but a very tall floral decor piece thing in the middle, it completely breaks the circle advantage. I think eye contact and your ability to convey body language is a major component.
I really hate trying to carry conversation in restaurants for that reason, and because the background noise levels can often get to a point where you can only hear the person sitting right next to you.
You're absolutely right that 1) group composition, 2) room structure, and 3) motive(s) are all important factors. As someone else observed, having a "discussion leader" is also important in that sort of setting.
Kind of the opposite as when you get seated at a restaurant in a long rectangle table. You immediately know it will be difficult to talk to the whole table and will have multiple conversations taking place. If you're at one end, you'll likely only talk to 3-4 people. If you're at the center, you might talk to 3-4 to the left and right but they'll be different conversations. Not that this is a strict law of table talk, just kind of what usually takes place. Sometimes there's something that comes up that gets everyone's attention and the whole table is shouting. An even more extreme example, is a bar top seating, where you are just a line facing the same direction. You might only talk to your neighbors and possibly their neighbor but it's not great at facilitating larger group discussion.
If you ever go to a banquet or wedding where they have round tables but a very tall floral decor piece thing in the middle, it completely breaks the circle advantage. I think eye contact and your ability to convey body language is a major component.