Yaris Sweet Spot

This seems to be a sweet spot:

Environmental conditions:
straight extraurban road
indicated speed around 70 km/h
HSI indicator on the exact half of the ECO zone

After an acceleration phase, with RPM over 1500, revs settle down a little over 1000.
SOC is slightly growing, speed is constant in the ending.
The road is slightly downhill, but only 5 meters over 1 km.

Let's substitute elevation with accelerator pedal position:

After the initial pressure, pedal was settled down on a steady position.

Maybe it's the electric motor that is helping the petrol engine keeping its revs down?
Let's see the electric aid chart:

Current is flowing only in the initial acceleration phase, not during the following run.

Here's the engine load:

It doesn't change significantly over the sweet spot.
We can also see that the sweet spot happens during the heretical car state.

Let's add fuel flow to the chart:

The flow has values comparable to the S1 phase.