GfxRectangle Positioning

I would like to draw a rectangle which stays with a bar as you scroll through a chart (i.e. same behaviour as with PlotText). Using the code below, the rectangle gets "stuck" to the left hand side of the chart as you scroll through the chart.


I must be making some very basic mistake here but looking through this forum and Google I can't figure it out! Any help would be much appreciated. Thanks.