Resizing docking panes

I've created a new docking pane theme and need to create more gutter space from the edges to where the panes are drawn (i.e. increase the buffer from the bottom and right edges to extent of the pane).

I didn't see any virtual functions I could over ride after deriving a class from CXTPDockingPaneManager.  I was curious as to how I could handle this.

I'm not sure why it's happening this way, but the client region of the frame for the docking pane manager is increasing instead of the client region of the docking pane manager.

I do have a CWnd as the parent for the dialog I'm creating.  I modified the OnSize function to redraw the CWnd and CDialog 5 pixels shorter and narrower.  I'd like to avoid custom drawing with OnCtrlColor (since we may be swapping out colors on the fly), so I didn't know if you had any other thoughts. 

This screen shot shows the 5 pixel buffer that is being colored with the default dialog background.  I tried modifying the extended window styles to have them as transparent, but that didn't work and caused some other painting problems.