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troops no longer block line of sight to each other. and they haven't been able to for nearly a year.
now they do a target priority test (a leadership check) not to fire at the closest target. vehicles still block los (skimmers don't) and ignore the target priority test.
nearly every army i've ever played would rather shoot down your war walkers than try and assault them. (the one exception is khorne who didn't have any weapons that were'nt boltguns)