The size has more to do with what tyou ROOM requires in terms of balance & scale. I suspect that if your wall is long and the sideboard is short, then to get this to work you will have to extend the appearance by adding chairs or art or both.

@BeverlyFLADeziner My wall is extremely long—running the entire length of the room with no doors, windows, or features beyond baseboard and ceiling moldings.

I have no use for additional chairs.

If you have a long wall does it possibly make sense to have a short sideboard?

You never expand the table with a leaf? Here are large dining rooms with tables and sideboards.

My table does expand, but it still seems to only fit six chairs. So...that’s all I bought.