Well there's a few problems.

First off, I do have an interesting background to my monitor, because it's set in front of a corner hutch. And I actually have a light set up directly behind it so that it's backlit. One problem is that my monitor is so large it fills up my FOV even when sitting fairly far back. I'm currently sitting approximately two feet from the screen, but I've played Portal at as much as three.

I haven't made the window any smaller via config files, but I am using the smallest resolution setting, which produces a window 8.5" diagonally. If it were any smaller I simply wouldn't want to play it because I wouldn't be able to see anything.

Even with all this, the very first training exercise that rotated me through a portal really made me queasy. I've been able to play a little more, but I can feel it building...