Is it a BUG when using OpenXR?

[SkyThinker]

I have been doing VR racing for a long time with OpenXR Toolkit. Tested games are ac, acc, iracing and dr2. The toolkit works perfectly with fixed foveated rendering to help boost my frame rate. In this game, though it is already well-optimized for VR, the toolkit seems broken that the range outside the center area which is supposed to be rendered at a lower resolution is missing a lot of track details, especially in street circuits. It's very hard to neglect the sudden transition between the two ranges. Is it a bug or a new built-in feature to help boost frame rate in corporation with OpenXR toolkit? Or how to turn off this feature?

[grzes19]

Use only 1/16 mode for middle and outer ring. Only this one works. I've set them at 43% both.