HEV EV miles are irrelevant. Even the downhill miles and regen miles derive from miles on ICE. But for the record, I believe the HEV battery capacity theoretically allows for 7 miles on EV.
But yes, you may not gain at all from the PHEV with high electricity cost unless you save significantly on the purchase price because of rebates. One other factor to consider though, if most of your miles are electric, there could be significant savings on maintenance.
2018 Kia Niro LX HEV Metal Stream - identical to Ioniq drivetrain