At the start of term banquet the other Gryffindor's won't sit next to Harry and there's a 4-5 seat space between him and his classmates - but only in the close-ups. In the long shots from Dumbledore & Umbridges point of view when they're giving their speaches you can pick out where Harry and Ron are sitting and Seamus is sitting right next to him with no gap in the seats.