Там в описании спелла же написано:
Да и теже коменты на вовхэде:ToolTip: While standing in the Power Circle, the caster gains up to 320 spell damage and healing.
Although everyone (in the party/raid or not) gets the buff while standing in the circle, only the caster himself actually profit from the spell damage gain. As of 2.4.2, this trinket does now only profit the caster. He still has to stand in the circle to profit from the 320 spell damage bonus (although the buff last abit if you moove out of the circle),
