Based on this question: Can I dismiss a spell one target at a time?
A follow-up. When are you considered "in range" of a spell's effects?
The SRD says:
If the Duration line ends with "(D)," you can dismiss the spell at will. You must be within range of the spell’s effect and must speak words of dismissal, which are usually a modified form of the spell’s verbal component. If the spell has no verbal component, you can dismiss the effect with a gesture. Dismissing a spell is a standard action that does not provoke attacks of opportunity.
But no range is specified. Is this the spell's original range? What if the spell targets multiple targets that can move individually? Say you cast Hide from Undead on 3 people and yourself, and two of them move away. Can you still end the spell because it's affecting you? Does the spell end for everyone, including those now out of range? Or must everyone return to touch-range before you can end the spell?