True line of sight is such a terrible rule honestly, especially with people kitbashing/converting/proxying models and thats without considering people making fancy bases etc. There is no way people will accept you blocking line of sight because you put a tree, tall grass or whatever on your base.
Im not sure how people are doing it at the big tournaments
@LizardWizard but whenever I play in smaller tournaments or with my mates it is kinda a gentlemen thing. Usually you can shoot whatever is within range, unless there is an obvious thing blocking line of sight, like a terrain hill/wall/building in, or if there is a huge model like a Greater Unclean One. I dont think any of our models are big enough to give reasonable line of sight blocking.