Mine is that engine speed for a 2-bar burn can be anywhere between about 1500 and 2300RPM, depending on load and SOC. Managing RPM is the key.
When first driving the C-Max, I spent a month developing a hybrid driving technique based on input here, before recording standard route data. My understanding was to "accelerate as fast as you can while still charging." As long as you saw a ^ above the battery, you were good.
As I thought about it, I realized in my case, this was a bad thing. I wasn't giving the battery enough charge time, so EV was limited. I started looking more at RPM than Empower bars, because I could hear the engine speed wasn't following the Empower display.
The next season, I tried to keep RPM below 2000, corresponding to a 1.5-2 bar burn in Empower, depending on SOC. I accelerated more slowly, but for a longer time, so average speed didn't change (still a 15 mile, 30 minute trip).
- mileage went up 12-15% (more benefit in warmer temps)
- fraction EV went up from 67% to 71%
Now... 2000 RPM many not get you up to highway speeds, or up steep hills. I'm driving 35-45 speed limits on generally flat land, so no one should take any of this as an absolute. Just think about charging time when selecting ICE run modes, and you'll gain EV miles.