The 2.64 I was referring to is the throw ratio (ratio of projector throw distance to screen height) for the BenQ - you might be thinking of the screen ratio (ie., 2.35:1).
What I was making note of was that with the 1070 and the CineVista lens (my CIH setup using an anamorphic lens), the greatest possible throw ratio value is 2.64. This value relates specifically to the design characteristics of the lens. In the case of the CineVista, 2.5 is minimum, with 3.0 to 3.5 optimal. Being so close to minimum in my case results in quite a bit of pincushion.
I wanted to respond to your request about using the BenQ in a CIH setup - yes it can be done - and likely other lenses could provide better results at these throw ratio levels, though they could be considerably more expensive.
As an alternative, I experimented using a 2.35 screen, the 1070, and my Oppo 103. I found that if you displayed the scope image zoomed with the black bars off the top and bottom of the screen, you could watch a 16:9 movie sized at almost the height of the 2.35 screen by performing a 1/2 zoom on the Oppo. Unfortunately, the Oppo will only do this with DVD/Blu-ray source, not with cable/sat/Xbox images.