Revit :: Mask Regions With 0mm Dimension?

I'm using a couple of masked regions to form symbol linework (so that it obscures background and shadows) in section.
 
In my screen family, I have a masked region that in theory could end up having a 0mm length - that obviously throws out errors.
 
The following screen grab shows the regions (at screen soffits) that are set to lock to the frame face and external wall face. Trouble is I have an instance parameter to allow the screen to fill the whole wall thickness (which also then toggles on architraves). This results in the 0mm. I have therefore done a slight 2mm overlap to avoid the issue, but this leaves a residual ovelap in the linework that looks ugly.
 
Setting the masked region to simply not display doesn't avoid the problem, Revit still 'sees' the errant 0mm.
 
Is there a way of having this masked region working in both options (ie when needed - locked to ref planes) and then not producing the error when the frame and wall are coplanar ?