When posting the original question, I never expected to generate such a lengthy discussion on EV+ either Thanks for all the insights and revelations!
I am seriously NOT a car expert at all. From what I can summarize by reading this forum and online materials, if you are a Ford marketing person, what do you think the average C-Max buyers are concerned about? I can think of three topics:
(1) How much gas do I save? (Thus so many discussions of MPG, 600-mile club, cover of the engine chambers, drifting behind big truck, avoid acceleration or hilly route, etc.)
(2) How long can the HVB last? (Thus so many discussions on warranty and consumer confusion of 12V battery and large HVB, replacement cost, etc.)
(3) I can't find a No.3 here. (Most other issues are related to 1 or 2, or not significant in comparison, or lesser a factor you considered when buying a C-max., perhaps power or comfort?......Again, sorry for my ignorance since I am not a car expert.)
So for me, the EV+ mode appears to serve the top two interests here (regardless whether Ford is promoting it this way). By using more HVB, you can drive a little longer on EV, and get higher MPG overall; also reduce the HVB level for (potential) long time storage. That is also my concern that when the HVB is too low, the next start will lead to ICE kicking in right away, and may lead to less gas saving and lower MPG
It is quite clear now that the HVB indicator is not accurate and the small difference is hardly significant or meaningful for topic 2. One way I can think of avoiding an "ultra-low" HVB storage level (if that were even possible!) is to avoid aggressively prolong EV driving just BEFORE EV+ comes up. This way, you expect a higher level of HVB before EV+, and thus a little higher level of HVB once you park the car. My current rule of thumb is observing the triangles more tentatively for the battery use or charge, and to maintain half or above HVB level before EV+ coming on (less than 0.4 miles in my case). Make sense?
Enjoy the long weekend!