AutoCAD 2010 :: How To Clip Circular Viewport To Existing Circle

As often done in mechanical drawings, a circle is drawn around a detail in the main drawing, and the detail is displayed somewhere else on the drawing on a larger scale.

My detail is the small rectangle in the upper right corner of the larger rectangle. I have also drawn a dash-dot-dot circle object around that corner to designate the detail-area.

In layout 1 the top left viewport displays the "whole" drawing. I also created a circular viewport to display the detail on a larger scale.

In the circular viewport, I used zoom-to-object (and selected the dash-dot-dot circle). The result is visible :both circles (object & viewport) are still visible, and they are not concentric too.

I thought the zoom command would have zoomed until both circles overlapped eachother and were concentric...