If the slab, footing and foundation in that view are part of your model, then any filled region you draw over the top of it is going to override/mask the intersecting part of the model.
You might want to select the individual lines of the filled region that overlap with the model and make them the same lineweight (thin, wide, etc.) as the model object that they overlap, rather than leave them as invisible lines. Not all boundaries of a filled region have to be the same lineweight/linetype, just in case you didn't already know.
If, however, the slab, footing and foundation are another filled region(s), then sending the invisible-boundaried region to back should work.
Ross Kirby
Principal
Dynamik Design
www.dynamikdesign.com