Output image looks blurry if using XYB and chroma subsampling other than 4:4:4

**Describe the bug**
I tried to compress a couple of images with XYB colorspace and different chroma subsampling settings, but found them all to be very blurry except for 4:4:4, and it seems that Luma is subsampled as well. Without using XYB there is no such problem.

Is this a bug? Or it is not recommended to use XYB and chroma subsampling together?

**To Reproduce**
Compress an image using jpegli with args given below.

**Expected behavior**
The output image should be about as crisp as the input image.

**Screenshots**
Test image: https://r0k.us/graphics/kodak/kodak/kodim21.png

`cjpegli kodim21.png kodim21_444.jpg --xyb --chroma_subsampling=444 -q 50`


`cjpegli kodim21.png kodim21_420.jpg --xyb --chroma_subsampling=420 -q 50` looks blurry compared with 4:4:4.


`cjpegli kodim21.png kodim21_422.jpg --xyb --chroma_subsampling=422 -q 50` looks blurry and stretched horizontally.


`cjpegli kodim21.png kodim21_440.jpg --xyb --chroma_subsampling=440 -q 50` looks blurry and stretched vertically.


**Environment**
- OS: Windows
- Compiler version: Not applicable. I downloaded the encoder from libjxl's latest CI artifacts https://github.com/libjxl/libjxl/actions/runs/14097851256
- CPU type: x86_64
- cjxl/djxl version string: JPEG XL encoder v0.12.0 b1842b9 [_AVX2_,SSE4,SSSE3,SSE2]