Before and after: https://acstuff.ru/u/comparison/NkI
I must say, this one was the thing that annoyed me the most about original Assetto Corsa. When the steering wheel reflects white and red curbs underneath the car, as you cut a corner, that’s just silly. It’s not perfect solution, as it always with cubemap reflections, but at least it would mask things below the car reliably. As for performance, takes 7–10 μs to prepare reflection cubemap for interior on my 1060 GTX, so, even better than I expected.
(Some more details about performance: of course, updating masking cubemap with interior silhouette is much more expensive, takes 0.5 ms (500 μs), but patch only does it when car is changed or when something like door animation has moved, so, basically never. For all other frames, it just takes main reflections cubemap and slaps that masking one on top, not forgetting, of course, to rotate it accordingly.)