This is a diagram that "adesant" came up with on the BKCII forum to help explain woods LOS and concealment. This was one big discussion during the con game. One reason I'm playing a quick scenario right now is to work through some of my thoughts on woods. As good as this diagram is, I'm going to go with woods and buas are both impenetrable. This means that you can only see in or out if you're on the border of the terrain feature.
I'm also trying out the rules that you can only shoot with the 90 degree arc when shooting in or out of the terrain.
In addition, I'm saying that you use any part of the base front to any part of the enemy stand to determine LOS. However, for LOF, there are three conditions. If you can see just the corner of the stand you will be able to shoot but will only hit on a 6. If you can see the middle of the nearest enemy edge, then you will hit on a 5+. If you can see the center of the stand then you will hit on a 4+. Terrain modifiers will overrule these to hit numbers. This allows for a unit to fire from behind terrain, hit the enemy at a 4+ and the enemy can only hit on a 5 or 6+. I'll have to work out a diagram on this.