[Phase]

Originally Posted by aerohead

1) I recommend losing the wickerbill. It's a downforce device, intended to create separation, not attachment. Especially not 're-attachment.'
2) I recommend that you not create a backwards-facing-step, ending the upper trailing edge at the taillight location. Aerodynamically, you couldn't possibly do anything worse to the car!
3) And as I've stated, since the IONIQ is already a 'fit' under the AST-III, the rear upper trailing edge ought to just follow the AST contour.
I can only guarantee 100% flow attachment.
4) The 'diffuser' should also follow the AST.
5) I don't have access to an IONIQ. I haven't a clue about the rear quarter-panel camber, or any vestigial OEM boat-tail tapering. If there is some preliminary tapering, it should take off from there, while following a 'french-curve' contour of the AST, as is present on the roof.
6) This is the most important thing you're going to be working with.

I will film an Ioniq walk around video and upload it on here soon and point out the area that need focusing. Searching online for Ioniq images doesn’t have much high definition detail I’ll admit