To use Relative X,Y Coordinates requires the at-sign @ (See below for examples):
X = @-1 Y = 0.25 would result in -1 (from Panel Right) and 0.25 (Y)
X = -0.5 Y = @-0.75 would result in -0.5 (X) and -0.75 (from Panel Top).
Add Fiducial Shape and then enter Width, Height, Coordinates, and Rotation. Here's a sample dialog: