Celik
There is no range specified in the description of Taunt power. As well, the red X is removed from the icon at 27m, but it still can't used until I'm within 25m. (These numbers are for Taunt 3, if it makes a difference.)
Range is indicated at the bottom of the action. Taunt 1 - 6 all show Range 25 meters and that is the range I've always been able to use Taunt.
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Eldest, Order of the White Lotus