Thanks for the A6.12 reference, that is helpful. However, I'm not sure it resolves my original confusion, because A6.12 seems to me to be limiting specific LOS-draws to specific circumstances. So you can only draw LOS to a hexside if you can take a snap shot (or bypass or whatever, but the other situations aren't relevant here). In turn, you can only take a snap shot if you are "a unit wishing to make a Small-Arms/MG Defensive First Fire attack". Since reserves can't fire, it's not clear to me that they are allowed to string the non-standard LOS.