Well I don't think those suggestions will make the turnout improve, maybe just give an idea how many will join in. But my main point is that if you run a social dungeon/fractal night and more than a full group turns up, you should just swap people out after every path, or go with groups that are not full with 5 but run a dungeon/fractal that can be done with 3 or 4. This is what we do at my smaller guilds regular fractal night and results in people not having to wait more than 10-15 min before they can join a path.
But if teams start running complete dungeons, than if you mis the call, you just as well don't show up at all