It's too bad the administrators of this forum and the equivalent (currently shutdown) C-Max Energi forum haven't merged the Energi forum as was supposedly planned into this forum yet so Energi owners can comment. You can also post your questions about how to best operate your Energi on the fordfusionenergi.com forum.
IMO, first you should assess how much usable energy (kWh not miles) is currently available for EV only operation on a full charge. This will give you a base reference as to how much capacity the HVB has lost and a reference to measure how much capacity fade (HVB degradation) you will experience over time. When new the HVB has a capacity of around 7.6 kWh with about 5.6 kWh available for EV only operation which would include use of the HVB for all electric power used in the car. For example, in the winter many Energi owners will not use the heater as it's electric until the gas engine (ICE) has been run so that the engine cooling system can supply heat to the cabin. Some simply never turn the heat on and just use the driver seat heater. Thus, in the first mile or two one might want to run ICE before switching to EV.
In addition, every time you discharge / charge the HVB, the HVB looses a little bit of capacity. So, you might want to use ICE more than you are currently doing or you might want to not charge the HVB to full capacity but only to the amount normally used every day. In your example, your wife arrives home with 4 miles of EV capacity left. Thus, rather than charge to full everyday, you might consider charging only to XX% everyday not 100%. Problem though, as I understand, there no way to automatically set an XX% charge level.
SOC = state of charge expressed as a %. So, when new and fully charged, the SOC = 100% or the HVB capacity is charged to 7.6 kWh. Over time, the HVB loses capacity. If after several years, the HVB has lost 1.9 kWh, the maximum SOC of the degraded battery would be 75%.
You cannot directly read SOC of the HVB unless one has a scanner to connect to the OBDII diagnostic port. So, one can monitor SOC, HVB temperature, and other variables while driving so that one can operate the car to mitigate battery degradation. Most owners don’t do this but those that do have minimized battery degradation.