Tiny JPEG preview in DNG converter when using JPEG XL

I'm invoking DNG converter 16.1 from the command line in Mac OS Sonoma 14.2. When using JPEG XL compression (e.g. with flag -jxl_distance 0.2) I only get a 256x192 pixel preview in the resulting DNG compared with a full-size one without the jxl flag. This seems to me to be a bug, or is there a workaround?

Command is of the form "$dng_converter" -d "$output_folder" -p2 -lossy -jxl_effort 4 -jxl_distance 0.2 /Volumes/Untitled/DCIM/source_file