We had a party of 6 this summer. In a previous experience with 6, we were at 2 tables (one of 4 and the other with 2 from our party and 2 from another). This summer, however, we were placed at two high top tables pushed together and only our 6 sat there. I did check in right away at the 2 hour mark and the person seating us mentioned they assign tables by how soon you check in. Note that you must be in or near the park before they let you check in. Having to be in close proximity was a surprise to us and we were just lucky that our dinner in DTD finished right around 6 pm. I believe I checked in at about 6:05 or 6:10.
Also, we learned that they will not seat you until you can show that you received the text message that your group was being seated.