"From the bunker" misses an important point

[Ranger REG]

Of course to counter concealment, use area-of-effect weapons. It gives a greater chance of hitting the person, since an area-of-effect weapon can cover more than a 5-foot square.

 

[takyris]

Or an automatic weapon -- you'll have to save no matter how foggy it is in your square. Cover will give you a bonus there, while concealment might make your DM give you a penalty -- if you couldn't see the guy pointing the machine gun at you, for example.

-Tacky

 

[Plane Sailing]

If a mook needs to roll a 20 to hit you, additional cover doesn't give you any benefit, but any concealment can help.

That seems a little strange to me, and it is one of the artefacts of a "natural 20 hits anything" rule. Perhaps using the optional "natural 20 means add 10 to the total 'to hit' would overcome this, but I'm not convinced.