How far should the party hang back from the scout?

[Nail]

Well, even more specifically, the traditional purpose of scouting is either to avoid enemies, which nobody in D&D really wants to do, or to wipe the enemy out with a surprise attack, which generally isn't feasible except at low levels thanks to the magic of hit points.

LOL!

True, too true.

 

[AuraSeer]

If we ever need an actual scouting trip, for instance if we approach an area where we suspect an ambush, we stop out of sight of it and send the ninja on alone. That's usually a distance of hundreds of feet-- several rounds' movement at least. We're not too worried about her safety. With gross amounts of Hide and Move Silently (about +25 or higher, last time I looked) she almost always remains undetectable. If she does run into a monster that can spot her, she's got invisibility and etherealness powers which are great for escaping.

In more common situations, the ninja walks about 30-50 feet ahead of the party. This is not to help her sneak up on monsters, but to help us stay out of range of any traps she may set off. (Big bonuses in Hide and Move Silently, not so much in Spot.)