I, too, would like to better understand the difference between Eco and Smart modes. My 2023 EX Hybrid defaults to Eco when I start it. For a good while, I switched to Smart mode but eventually stopped because I could see no difference in performance or economy. I now leave it in Eco mode unless winter conditions dictate Snow mode. (I am retired and rarely go out in bad road conditions.)
Several months ago, I took the Kia to the dealer for some sort of software update. Since then, the mileage has noticeably improved. I was already getting close to the 38 MPG the EPA predicted. After the update, I am consistently getting over 40 MPG per tankful, often over 42 MPG. If anyone got the letter about the software update and have not taken the car in for it, I highly recommend it, There was no cost for it.
I am especially pleased with the mileage I get because I live in the higher mountains of West Virginia. The mountains here are not as high as out west, but they are steeper. Driving up steep hills is tough on fuel economy.
Wayne