I have struggled with the lower right section of this painting for quite a while.  The last solution (up to now) involved some lines that echo the curve in the upper left.  One small one in particular butted up against the black rectangle in the lower right corner.  I drew and re-drew that line over and over, but it didn't work.  There was a lot of paint on that little shape and the surface was raised anyway so it was getting out of hand.  Finally, I decided to get rid of it altogether and extend the stripes over to the black rectangle.  I assumed I had glued foamcore or another layer of plywood to the surface to raise it so I started cutting into the edges with a matte knife and then tried to pry it up.  I wasn't making headway fast enough so I got a joint knife and hit it with a hammer to cut deeper and then lifted with the knife.  Imagine my surprise when I lifted off a chunk of wood to reveal the wall behind the painting.  Uh-oh.

Ah well, nothing a little foamcore and modeling paste can't fix and off we go...