This issue has persisted since Forza Horizon 3, but in reality dates back to… the first Forza Motorsport on the original Xbox. The S14 Kouki model reuses the body of the inaccurate S14 Zenki, but replaces the front end and the aero package for Kouki Aero parts. This creates a painfully disproportionate model, almost worse than the FM1 model it is based on.
Apart from the front end up to the windshield/fenders area, all body line inaccuracies are identical to S14 Zenki’s inaccuracies. The whole front end is painfully inaccurate. The headlights are too big, the lights in the bumper and the air ducts are too big, the bumper itself is too big and more “in line” with the side skirts than it should be.

The rear end consists mostly of Zenki’s inaccuracies, such as disproportionately huge taillights, but with the Kouki Aero kit came in some new ones. The rear bumper itself is too small, which is especially noticeable in Forza games that feature license plates, because those change size on this particular bumper compared to other aftermarket part options.
Mind you, this car debuted as paid DLC in 2016, together with many other Xbox 360 and original Xbox models. This car, as well as all reported inaccurate car models, needs a complete rescan.