Fuel Economy - What do you get out of a tank? (3rd gens only)

[ShadesLE]

My newly purchased '03 TL VRX LE 5 spd has been sitting between 11.4 and have just gotten as low as 11.1 L/100km.
Bog standard car, driven mostly easy with a few short overtakes, etc on a combo, but mostly hilly, windy country. Hasn't been loaded at all.
I live up a windy mountain road, and have been using on the weekends just for a run. Usually leave it in 5th mostly (my daily is an 86 Skyline 5spd which bizarrely seems happier to sit in 5th to even lower speeds, so I am still used to that). Easy on the throttle mostly, smoothest changes etc.

Would this be typical roundabouts?

[testedandbaked]

Verada KH getting around 18-19L/100km city driving, terrible. Swapping out the O2 sensor hopefully fixes it.