I now understand the cross-hatched area as area that the 28" MH721 can't reach.
Looking at the situation more this is what I see:
As a plotter with pen installed, I take it off line and origin set (0,0) on plotter display when carriage is all the way to the right.
Next using SB with origin set at either lower left corner of cross-hatch area or lower left corner of border of the circle ( using the set origin window), the carriage always travels to x=3822, y=3957 as displayed on the MH721 then starts plotting. This is with and without "Fit to Origin" box checked, no difference. The plotter allways starts plotting well into the workspace.
What gives?