Day One Hundred Ninety-Two: Really? That's the problem? You've gotta be kidding me!
So, the problem with the white background was NOT a shadow from the irregular ceiling. It was the shadow of the white background wrapped around the frame. I can't believe it took me that long to fiture it out, but that's how these things can be sometimes. You just need to go away and come back and try some things before you realize the problem was staring you in the face. Bonus points if you figured it out before getting here.
Extra credit: Why is my background not white? It looks like it has a hint of brown. Is it a) the ceiling lights (which were on brighter than yesterday), b) that the side flash was bouncing off the nearby brown wall or c) all of the above? This time I don't know the answer today. Perhaps I'll figure it out tomorrow.
Also, can't wait to use the soft box. I could use a less harsh shadow around my nose.