I was at bethel for a few years back in the 70's, and almost ALWAYS the tablehead was a elder, sometimes there just wasn't any around (dinner time) so some brave up-and-coming guy would need to sit-in, but it was rare, not forbidden.
Morning was assigned seating, afternoon and dinner you could sit anywhere. If you didn't show up for breakfast, you could expect a visit to your room right after the closing prayer by your tablehead. Table heads would decide which way the food would be passed after the first prayer (some guys would try and sit to the left or right of the head to get first picks on the food, so the head would decide, "we'll pass this way tonight" to prevent that sort of thing).
I always felt the meals were very much like the military would eat, so never had a problem with it, and most visitors I ever ate with loved the style and being part of the whole "bethel thang".
The food was always pretty good, and REALLY good the afternoon of the Gilead Graduation. They would let us off work a few minutes early that day. Some, mostly couples, would go to their rooms for a glass of wine or something with friends before going to the dining hall. You could almost always expect to have something special like prime rib on that day. I remember one graduation meal when Freddy Franz thanked Jehover for everything on the menu...carrots, peas, etc.