[aerohead]

The aeronautical engineer who 'invented' what we know today as 'Air Tabs', created them to solve the 'problem' of detached flow over the boot/trunklid of his Honda Accord notchback.
The VGs created the tiny, high-suction, delta-wing vortices employed by the likes of the Concorde SST and Space Shuttle, to help induce the turbulent boundary layer to remain attached down the backlight, enough to reattach onto the rear of the car, before leaving the car, capturing a separation bubble, isolated from the rear panel.
The small amount of air crashing against the top of the boot, provided a higher static pressure just ahead of the 'new' separation line, and when the flow separated at it's new location, it exposed the 'base' of the Honda to a higher pressure than would exist, had the flow been totally trashed.
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The key to a VG's performance is that, it have some 'surface' downstream, on which the flow may attach.
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The IONIQ has no such structure.
Also, the area you've marked already has a burst edge, from below the taillight lens, down the slanted side of the rear fascia.
You don't want flow attached in there, as it's prone to bistable flow ( hunting separation line/ acoustic 'booming' ).
My opinion would be to ignore VGs. There a solution to a problem that you don't have.
Your call.