I am trying to detail an extruded circle using Model Items.  The problem is the extrusion distance extension lines are attached to the center of the circle (See below).

I can drag the end points of the extension lines, but I can't "snap" them to the corners.  I end up with extension line gaps that are not equal (See below).

  If I create the dimension with smart dimensions I get what I am looking for, but this seems to defeat the point of creating the model dims in the first place.  Am I missing something?  BTW I'm using SW Pro 2009 SP5.1  Thanks

Dan