Hey John,
If you manually (with gamepad, jog pane or Manual pulse generator (mpg) pendant or with manual data interface (mdi) commands) go to the outermost corners of the work area, this always refers to the center of the bit. You can then add the radius of the bit to this to know how much you can mill beyond the work area.
However if you create a toolpath, the CAM program will take the bit radius into account. You will then either have to manipulate (fake) the bit radius setting in the CAM program, or the postprocessor, to mill beyond the machine limits settings for the workarea.