ockham, the seams are usually "small" in relation to the model surfaces. The size depends on the resolution of the rendered model (how many pixels are rendered for the seam-faces). In the above example, the seams are 0.2% to 3% of a box edge. The bottom right example has 5% seam width, a subdivided coplanar seam, and additional seams for the corners. Basically, Poser renders a highlight on the bright side of the normal, and a shadow on the dark side of the normal. Smaller seams create smaller highlight/shadow zones, and the edge renders "sharp" like a blade. Wider seams blur the edge contour, and the edge appears to be slightly rounded. Hope this helps.