rectilinear #3D rendering always takes a guess where your screen is, relative to your eye.
i say, "eye," because rectilinear rendering assumes you only have one.
so if you have one eye, and know where it is supposed to be (usually right in the middle, but distance to screen is a shot in the dark) and you keep it right there relative to your screen, rectilinear rendering won't create distortion.
problem is, you don't.