NEX6 focus appears to be horizontal...
I couldn't find anything in the manual warning about this even though I know it's fairly common. Wether using CDAF or PDAF, the NEX6 can't focus on something that is purely horizontal detail (such as smooth venetian blinds). Turn the camera 90 degrees (or even 20 degrees) and it focuses right away.
It's like the AF "sensors" are horizontal (they see vertical contrast.) I can see how the PDAF sensors might only be one orientation, but it's surprising the CDAF acts this way. Looks like this technology (both CDAF and PDAF in NEX) still has a lot of untapped potential.