Fuel saving by Super-Plus?

In expensive times like this one gets to ponder. The Yaris of my wife (is moving almost only in urban traffic) I filled with Super-Plus in early April to test whether and how this affects the average consumption. To make it short, the Reichenweitenvorsage (Range) went from almost 600km up to about 650km (remote indicator compared to the already driven kilometers). That is clearly more range than Super-Plus costs compared to Super. Yesterday I got e i refuelled (again Super-Plus) and after 648 kilometers driven 38.2 liters in tank, display range new 645km. Who has similar experiences? Yaris, 1.0Liter, May/2005, four-door with climate