Sorry, I don't think I made myself clear. my question wasn't about blocking line of sight to other models like page 18 says, its about blocking line of sight to itself... I know, I know, its absolutely ridiculous, and I'm not suggesting for one moment that we should expect any reasonable person to try to do that. Its just not everyone who plays is reasonable, and where ever there is a grey area, somewhere along that grey spectrum is a circumstance that is reasonable and confused by a gap in the rules.
As you said, page 8 describes the specifics of line of sight. Say you want to shoot a banner barer through a window from a distance. All you can see through the window is Banner, and the other play says the specifically placed the banner barer at the angle they did because they thought that were the banner not there, you wouldn't have an angle on him... but because the banner is there and your not sure.
Rules say you cant target the banner. There's no way to be sure that you could see that guys body through the window without turning the model, and the other player says that he put the guy the way he was in order to be out of sight not thinking the banner would confuse the matter.
I've got a Grey Knight unity with a banner, its massive, it could easily get in the way with a view through a window. Its not a problem in my case, because I happen to have magnetised the banner so I can change weapon load outs. so I could just pull his hand off... problem solved. Even if they shooter was saying, I think I can hit a guy from the same unit behind the banner barer, not a problem, you just move the banner guy, because he doesn't block line of sight to other models in his unit.
In most instances, its not likely to come up, but with the number of people playing the number of games they do, and with the amount of interesting conversions people come up with... I can just see there being times when people going... 'well do you think I can see him or not, because I think I could see him if that stuff wasn't in the way'. Thanks for your feed everyone, its really nice to post something on a public forum and not have it incite rioting. I asked my own group of friends in our facebook group, and 2 of them took it a bit seriously, but it takes all sorts to make the world go round a guess eh?