the voice command applies the skill against the creatures taht are in the area range.
Also remember that monsters are dangerous for a reason, simply yelling at them won't make them go and jump over a ledge , this is a skill not a spell like ability, otherwise it woudl be used the same against pc's whjo would be "taunted" to their deatshs. so don't rely on the mechanical side of that.
Just think of it as how Spiderman (tm) does with his oponents, saying annoying coments and making them angry so their minds got clouded by anger. This of course its just an example.
Hope it helps to clarify it.