so i kinda new to this site and sent a email in for clarification about hte obscurity rules here is the response i got back

Hi James,

Determining whether a mini is obscured is really a two-step process. First, at the beginning of the game, players must agree upon what pieces of terrain provide cover for what units. The general rule is that if terrain covers 50% or more of a mini when that mini is placed directly behind it, that mini will get cover from that terrain. This is where the AT-ST suffers; there are not many terrain pieces which cover 50% or more of an AT-ST.

The second part of determining whether a mini is obscured comes during actual gameplay. During this stage, if line of sight to ANY part of a mini is blocked by a piece of terrain, it counts as obscured. In many cases, LOS to part of the AT-ST will be blocked, but it’s usually blocked by terrain that can’t protect the AT-ST because it was determined that it does not provide cover to the AT-ST back in step one.

Essentially, the AT-ST is so large it will rarely have cover, unless that cover is “area” terrain like woods, or a particularly tall building.

Yep the first few iterations of the RRG have helped clarify some of the issues with terrain and cover. It's worth finding each version as changes are highlighted if you were working off the back of the printed rules.

Yep. Talk it out with your opponent. It a building is as tall as an ATST we usually give it cover, because even a ruin will block a lot of sight towards it. Of course, troops should be pretty good at moving around the building to get a clear shot if they need it.