I don't really get the grill size to # of people comparison. I think I read the q1200 claims to feed 8 people? Do they make that claim because you can fit eight small hamburger patties on the grill, or eight small bratwurst?
On the q1200, cooking for myself, I can fit one cowboy / tomahawk steak on the grill, along with an ear of corn and a big piece of broccoli. The outer few inches of grill surface aren't usable, since the lid will contact any food near the edge, and that's gross.
On the 22.5, I can fit six half racks of ribs, standing on edge, with about half the grill surface "off" the coals. I once direct grilled six chicken breast and it was crowded, there was certainly no room left over for cooking some veggies, or garlic bread.
So, I'm not a good judge of using grill space efficiently I guess!