Despite many lines asking your preference it has been my experience that doing so had little bearing on what table size you were assigned. Basically the information on passengers is transmitted to the ship and the person in charge of the dining assignments who then fits it all to thier dining room scheme the best they can. The only way to insure that you get something you prefer is to make your way to the area, usually the show lounge, where the Head honcho's are available handling dining changes. Your personal request placed in person is much more likely to be achieved and you can also see before first dining what size table you have. You can also be assigned a large table and only have two other people, depends on factors such are how booked ship is and so forth.
George in NY