For a long time, there's been a thorny issue locally, with regards Skimmers and Pop-Up attacks, and how terrain affects it.
I've been using a literal interpretation of the rules, which isn't that well received.
Take the following situations between Unit A (Skimmer) and Unit B (target/overwatcher). For each character, assume approx 5cm of distance.
1) AXXXXX__________B (Obviously, LOS)
2) A__________XXXXXB (Obviously, no LOS)
3) A_____XXXXX_____B
4) AXXXXX___B
5) XXAXXX_____B
6) A_XXXXX_B
7) A___XXXX|X_______ B
A_______X|XXXX___ B1-2 are obvious, according to the rules. The problems with 3-8 are the way the Skimmer Rules are written.
EA Official Errata for 2.1.13 wrote:
A skimmer that has popped up is assumed to be flying high enough that nearby intervening terrain that is closer to the skimmer than the target does not lock the line of fire. To check if the line of fire is blocked, simply measure the distance between the skimmer and the terrain, and then measure the distance between the terrain and the target unit. If the skimmer is nearer to the intervening terrain then the line of fire is not blocked. If the skimmer is further from the terrain, then work out the line of fire normally. If the distance is is equal, then both the skimmer and the target unit can fire at each other, but they both count as being in cover and the cover to hit modifier will apply.
The problem, for the most part, is reconciling this with the LOS rules which state you can see 10cm into a terrain feature, but you can't see THROUGH a terrain feature. So if the midway point is in a terrain feature, does it matter which side of the equation it's on? Examples 7 and 8 show situations where LOS terrain is an issue.
It might be intended that you track LOS (but not firing distance) from the midway point, and I'd be fine with that. But that's not how the Rules As Written seem to be intended. And can lead to some wonky situations (moving closer to LOS blocking terrain to get LOS, or further away to deny LOS, which seems contradictory).
Morgan Vening