As I understand it, the NAH's hybrid transmission is actually made for Nissan by Toyota (or at least is identical to the TCH's). Nissan's ICE is, however, not the same as the TCH's ICE. Apart from its slightly larger displacement, the Altima's ICE is not an Atkinson/Miller-cycle engine, and thus does not have the efficiency advantage of that design. Nissan also does not have Toyota's ten years' worth of hybrid experience, and this probably is reflected in their hybrid programming. I'd expect these to be factors that might also be responsible for any lower FE performance in the NAH.

Stan