The EPA data file has the Prius Eco ~3.5mpg ahead of the Ioniq Blue on the uncorrected combined mpg rating, but somehow the Ioniq is ~2mpg ahead on the corrected rating.
https://www.fueleconomy.gov/feg/epadata/17data.zip
That seems kind of strange, but INL testing should hash things out, assuming it isn't cut by the new administration.
https://avt.inl.gov/vehicle-type/all...n-architecture