As first a reader and later a writer of Regency Romance novels, I discovered there was a specific order for guests to sit at a table during dinner. The host sat at the head of the table, with the highest and 2nd highest ranking ladies on either side of him. The men not related to the hostess sat on either side of her at the foot of the table—usually husbands of the women sitting by the host. The lower ranking people sat in the middle of the table, unless the host and hostess sat in the middle and the lowest ranking sat at either end.
Early in the century, in some places it was still customary for have ladies sit on one side of the table and gentlemen on the other. Later in the century, hostess’s whim determined seating assignments, like formal dinner parties today, and gentlemen often escorted their table partners into the dining room. There is a letter from a Regency lady complaining about the “new” way of going into dinner two by two, “like animals going into the ark.” Later in the Regency, it became customary for men and women to sit by each other.
I also read a reference that it was considered rude to speak to someone seated across the table, but either that wasn’t true, or has been ignored by the movie producers and novelists of our day.
Quite a few records indicate there were more men than women present, and that people chose where they wanted to sit. That may have been the hostesses’ prerogative, especially if the dinner took place in a relatively small dinner at a country house. The formal seatings and settings were for formal occasions—generally in town, meaning London. I imagine that’s when having an even number of men to women became important.
I often refer to seating in my Regency romance novels and have the heroine note who is escorting her to dinner in relation to her rank, and sometimes in relation to where the hero is sitting. It can be a fun way to increase the tension, or merely another detail in painting a vivid Regency feel.
I found my image here: http://commons.wikimedia.org/wiki/File:37_quai_d%27Orsay_salon_des_beauvais_1.jpg