I don't recall anyone who has documented / described the hybrid mode operation in the Energi. I would think the hybrid mode algorithms are the same except perhaps threshold levels in the Energi might be increased - but why? running ICE just to charge the big HVB (in positive split mode) even now with low gas prices would likely cost (in Phoenix with about $2.64 / gallon) over twice as much to charge the HVB with gas vs electricity. But when descending a hill in the Energi, it makes sense to maximize regeneration whether the car in in D or L. So, ICE should not spin in L to slow the car down like in the Hybrid.
A bit off topic, so for those who don't care about the Energi - just skip this!
From what I can tell, the Energi uses the same (fairly small) range of battery that the conventional C-Max uses, when it is in what I call "highway mode", which means the larger part of the battery is depeleted, or the owner has set EV Later (which reserves the larger battery for later off highway use). I think Ford just copied the algorithms between the two. It makes sense, as you note, because there is no point in charging the HVB past a certain point - it is just burning gas.
The only difference I can tell is that the Energi will often not spin up the engine in L, because it has more capacity to store energy, and that it can recover extra energy on large downhill slopes, which it then burns off in either EV or just assisting the engine. After any excess is used, it reverts to that same highway mode.
I follow this forum because there is a lot of stuff the same between the two models. I try to think twice before posting, to make sure my Energi doesn't operate differently than the C-Max. I don't want to waste people's time reading stuff that doesn't apply.