The "current" evars can only be evaluated with a !parseEvars bang. The setting above is loaded only once, at startup, when the "current" evars are probably not even defined yet. In order to do what you want to do, you'll need to use a transparent xlabel instead, and set it up so that the label resizes when the tray does, e.g., with an !xTrayOnResize event bang or the like. Have the xlabel onEnter and OnLeave events fire off the XtrayShow/Hide bangs to make it behave like a hotspot.