[aerohead]

It's kinda slow @ EcoModder, so I went ahead and crunched the numbers based upon the 1st-approximation values.
1) 80-miles / 60-mpg = 1.3333-gallons/ hour
2) 1.3333-gallons x 111,836-Btu / gallon ( E10 REGULAR gas ) = 149,114.66 Btus / hour
3) 149,114.66-Btu / 2546-Btu/hp = 58.5682-hp gross input energy value
4) 58.5682-hp x 0.40 ( estimated engine thermal efficiency ) = 23.4272- Brake horsepower ( bhp )
5) 23.4272-bhp x 0.978 ( @ est. 2.2% accessory losses [ Argonne National Laboratory ] ) = 22.91188-hp
6) 22.91188-hp x 0.95 ( 95% transaxle mechanical efficiency [ Argonne National Laboratory ] ) = 21.766286-hp Road Load
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7) 21.766286-hp - 11.5347-hp (rolling-resistance [from original calculations ] =
10.231586-hp ( aerodynamics )
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8) 10.231586-hp = 117.333 feet/second velocity / 550- pound-feet torque/ horsepower ( 0.5 x 0.00238 slugs x Cd ? x 24.223-square-feet frontal area ( estimated @ 85.5% of gross area ) x 117.333 feet/second-squared )
9) solving left side outside parentheses algebraically: = 47.96069563 = right side of equal sign ( 396.8398168 x Cd? )
10) or, 47.96069563 = ( 396.8398168 x Cd ? )
11) divide each side by 396.8398168
12) 0.12085 = Cd (unknown)
or, Cd 0.1208 satisfies the condition for 60-mpg @ 80-mph.
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13) Since we're talking about profile drag, examining the profiles of vehicles exhibiting Cd 0.1208 may provide insight into the architectures which generate this coefficient, or near it; and the kinds of features the IONIQ might benefit from.
Some will be Bonneville streamliners, solar cars, and SAE / Shell marathon racers, of shapes that wouldn't necessarily lend themselves to a passenger car:
* JCB Dieselmax , 2018, Cd 0.117
* Goldenrod, 1965, Cd 0.117
* MANTA, MIT, 1995, Cd 0.12
* Autonoma de Mexico, 1996, Cd 0.12
* Honda Dream, 1990. Cd 0.12
* MG EX 181, 1957, Cd 0.12
* Walter Lay, Model#22, 1933, Cd 0.12
* 'Baby 'template'', 2017, Cd 0.1209
* GM Sunraycer, 1987, Cd 0.125 ( as raced )