I've been thinking about Tau Smart Missile Systems for a while. In 4th edition smart missile systems were brilliant, because you could simply hide all your tanks and pepper people with a mass of smart missiles.
Because they fly around terrain, your targets never got a cover save unless they were actually IN cover. However, in 5th edition where everyone seems to be constantly firing through cover, people have been getting cover saves against smart missile systems because they're firing 'through cover' when before they didn't.
I just accepted that this was the way things would be until there was another Tau FAQ or a new Tau Codex...
...until Raptor 1313 replied to one of my Imperial Guard battle reports stating:
"Page 27: the target can count the benefits of the cover they are in, or are touching it if it lies between them and the firer."
Now, everyone take out your Tau Empire Codex and find page 27.
Here is the exact wording from the Codex (sorry GW, but important rules are at stake!)
Tau Smart Missile System RulesThe smart missile system fires self-guiding missiles with the intelligence of a drone, which first search for then hunt down the target, passing around any blocking terrain.
The smart missile system can engage any target in range regardless of whether there is a line of sight to it or not. The target can count the benefits of cover they are in, or are touching if it lies between them and the firer.
Ignoring the bit of fluff (because sometimes this is contradictory) and sticking to the second paragraph, which is pure rules, it states that: