Confusion abounds in “gear ratio” as regards good fuel economy.

I suggest talking about MPH for each 1000 rpm, which takes everything into consideration, including tire diameter.

As regards getting the “right camshaft grind” for fuel economy, that is especially tough.
Today “variable valve timing” certainly improves late model engine fuel efficiency
but adjusting “ground in camshaft values”
down to what VVT is truly doing to the valves in today’s “real world”
is nearly impossible because even today’s 1800 page FSM
does not have tables about what modern PCM software commands are making happen to lift and duration.

There is another 10% fuel economy improvement if the air to fuel ratio goes from 14.7 to 18 or more.

There is an old Autospeed.com article about the early year Australia spec Honda Insight
and how at steady cruise speed on a level highway its air to fuel ratio would lean out to 25 to 1.