I am pretty sure the way the block mounts it puts the bow of the block directly in line with the way the chips are under the IHS. This way you are making more contact with them for better heat transfer. All blocks, with bows at least, seem to work better in one direction versus the other. This is why Vapor noted that the Heatkiller got better results in one direction versus the other. It doesn't mean you can not orientate it the other way, just that to maximize the block it's better this way.