Ya, your uncle driving paired with 0W20 will probably improve your FC even more. But I've seen your version of "uncle driving". I don't think it'll improve that much more
And ya, I like the Iriz a lot more than the Myvi or Axia. But only the 1.6L Premium / Exec interests me. The only thing I find interesting is the 40k km CVT oil change interval. That's really short. Why is the P1 CVT oil change interval so short compared to the Nissan ones? Nissan is 100k km.
As for FC, I don't know. Personally the FC on my current car has yet to exceed 11km/. Have not tried outstation driving yet.
Ya about that.... I realized it was opened, not closed as I originally stated. So I mixed it with the old oil I had lying around and used that as flushing oil.