I think I know the answer to this, but it seems unintuitive and it matters for a game I've got coming up, so I thought I'd throw it out here. Couldn't find it with a search, apologies if it's a duplicate.
Can you use Look Out Sir against Beam psychic powers?
As I read it, no you can't, for the same reason you can't use it against Perils of the Warp or Gets Hot. Beams strike specific "models", not units, so the wounds are not "allocated" as described on page 15; and the Look Out Sir rules seem to specify that only wounds "allocated" in this way can be intercepted by Look Out Sir. So it would appear that you can snipe characters to your heart's content with Beams, and they can't do a gosh darn thing about it.
It's just that while the lack of LOS is intutive for stuff like Gets Hot, it seems a bit weird when it comes to flying boulders, which you would think would be easier if anything to shove sarge out the way of.
Anyway, it matters because if it's correct that you can't Look Out Sir against Beams, the Assail power goes from being sort of moderately useful to being a potential game saver, situational but a real ace in the hole. All you have to do is single out a character - through a wall or engaged in combat, no less - and pass a wound roll, and even if they save it, they're down to half Initiative until the end of THEIR next turn. Oof.