1000R means you can place the screens in a radius of 1m and it would result in a circle with a diameter of 2m, thus
with the 1800R the circle would have a diameter of 3.6m. The 1000R curvature is ideal if you are sitting closer to the screens as the curvature is more pronounced.

If you sit at a distance of 1m, the image should appear rectangular again with the 1000R. The curvature is practically twice as strong as with the 1800R.