Where is walker LOS taken from - the base - or the viewport? Taken the rules as read it should be fom the base - it came up in a game last night - my walker had a unit bang to rights, but my opponent argued they had cover since the LOS was from the base.

LOS I believe is always taken from the top of the middle of the miniature. (Checking for obscured LOS is taken from the middle of the base though.)

Pg 41: "He does this from a viewpoint at the center of the attackers base at the top of the miniature. If no part of the target miniature's figure can be seen, then LOS is blocked."