@User: The end-of-line shortening then explains the specific rule about contact overlaps in one direction. But mask misalignment used to be the reason that all contact cuts had to be surrounded on all sides by metal. Most modern back-end process rule sets, especially for 0.18um and down, no longer require a metal surround on all sides for anything that isn't a thick top metal layer. Is that due to better alignment, or something else?