To clarify this further - at least in the Toyota family of hybrids, which of course includes the Altima - when you let off the accelerator you DO get regen effect, but it is only mild, simulating what happens when you let off in a non-hybrid in "D" and there is mild engine braking.

If you routinely use "B" mode, you'll see a decrease in FE, as part of the braking energy is absorbed by the ICE as Talmy noted, rather than shunted to the battery by necessarily stronger regen braking.

Pete