Warhammer 40K Tabletop VII: Common Sense is not RAW.

[crazedloon]

There are plenty of rules I haven't heard of yet, but that doesn't mean they don't exist. It's a learning game. However, it makes perfect sense as to why it'd be a rule; denying LOS is the biggest element to surviving a Shoot phase. There's all kinds of shenanigans that could be undertaken using models built specifically to screw with LOS, and that is, quite frankly, rather unfair.

true only to a point. Because you must remember if your opponent can not see yo than you in turn can not see them.

The only time this can be abusive is if you model everything so just their head can be seen. Than you get a cover save but your opponent does not. However then you are tailoring to specific terrain and outside those pieces you are once again "even."

also this abuse is not even all that great since people already manuever their men to take advantage of cover (hiding half the unit behind cover while the other half can still shoot). Indeed its this sort of thing that makes me prefer area terrain. Anything in area terrain gets a cover save (so it comes down to if the model can see and if you can see you can be seen) and anything behind normal area terrain (which tends to be around 6" or more) still gets that cover save so no modeling shenanigans.

So at best if you have modeled an entire army ,on knees for example, the best you get is half your unit can now shoot (where half was wasted from hiding) or nothing can shoot and you best hope your opponent deployed foolishly close to the "abusable" terrain so you can assault.

Also to make sure I am not talking out my rear end I gave the main rules a quick skim and saw nothing on this "LoS rule" which seems to support the fact it is some local shenanigans

edit:

That was the rule for bases, back in fourth edition. It's one of the many things that changed in 5E, and nowadays if you're using a non-standard base you need to check before the game that your opponent doesn't mind.

well that is a dumb change, but presumably it is to avoid so abuse a larger base may give... (only a few things can actually gain anything from it)