I would not only find this annoying but call it a defect. The top segment is there for a reason and when full should indicate. Mine goes way longer than 4km before dropping down one segment.
I'm not 100% sure how the fuel sender works, but it seems as if the float is adjusted too far up, so it is overly sensitive on the top end (barely registering full when tank is full) and less sensitive on the bottom end (having one bar on when reading empty.
I can't recall (my bike just got uncovered from its winter nap) but I thought when the last bar appears the fuel icon lights. When the last bar disappears the fuel icon flashes.