That's a good question! It actually doesn't matter if the circle is symmetric or not, or what shape the table is, unless the table is a strange shape like this:

The problem with this table is that A could be considered as sitting next to E, and D could be considered as sitting next to F. As long as the table preserves the "neighbor arrangement" of the chairs, it doesn't matter what the shape is.

Please don't hesitate to ask if you have any more questions!

Happy Learning!