If you're driving a PHEV, then with a full charge, you have an approximate 26 mile range. When you've depleted that range to 0 miles, you're likely to observe a 20% state of charge reported on the instrument console. The car drops out of full-time EV mode around 20% state of charge (SOC). The car depends on the traction battery to start the ICE, so driving the battery to 0% SOC would be a disaster, because you wouldn't be able to start the ICE (and it would also be bad for battery "health" to let it deplete to that extent). Essentially, the PHEV begins to behave like an HEV when the PHEV battery hits 20% SOC. Or you can invite the car to begin behaving like an HEV sooner than that by toggling the EV button while there's still more than 20% SOC in the battery.
When you are looking at the EPA numbers, I believe you are looking at the KWh that the charger consumed to increase the charge from 0 miles EV range to 26 miles EV range, and SOC wasn't a consideration. I don't recall for certain, but I think the EPA numbers measured the KWh consumed by the charging device, not the KWh absorbed by the battery.
2018 Niro PHEV Gravity Blue