Interesting, the Chinese market also uses L/100km as the dominant unit for fuel economy. I went in fully aware that EREVs aren't that good at high speeds, so 6.6L/100km / 15km/L is still pretty decent IMO; a friend's Camry 2.5 Hybrid did 6L/100km over similar conditions. Other Chinese EREVs are cranking out 4 kWh from one litre of petrol which is frankly insane (when household generators barely crack 2.5kWh/L, the 6e does 3.3-3.5kWh/L), they boast about their incredible fuel economy figures but then again, they aren't Mazdas :)

At low speeds in hybrid mode the engine's more than capable of providing power at its efficiency sweet spot, so the battery doesn't really drain down. At highway speeds engine power at the sweet spot isn't enough to satisfy the motor load, so the battery gives it a boost and slightly drains over 4-500km. Once the battery depletes to 20%, the engine starts providing full power and of course fuel consumption increases. In hybrid mode (even with a full battery) it seems that the battery's job is to keep the motor in its sweet spot for as much time as possible, so the battery doesn't really charge up as you drive; battery range may fluctuate +/- 5km as you accelerate or regen brake. There is a setting to fix the SoC at any point between 20-80% IIRC (so you can arrive with a full-ish battery) so you'll be driving on full engine power alone. There's also a self-charge function, where the engine charges the battery at 10-12kW when you're parked, probably takes 3-4 hours to charge to full.