Question about RaBitQ and RaBitQfs

[Luciferre]

I tested RaBitQ and RaBitQfs on Intel machine, here are the results:
IVF16384_HNSW32,RaBitQ
cno=-1 key= perf=0.0000 t=0.000
cno=0 key=nprobe=1,quantizer_efSearch=4 perf=0.3312 t=0.109

IVF16384_HNSW32,RaBitQfs results:
cno=-1 key= perf=0.0000 t=0.000
cno=0 key=nprobe=1,quantizer_efSearch=4 perf=0.3328 t=0.498

for 1 bit, RaBitQfs is slower than RaBitQ, similar for 4 bit and 8 bit. Is RaBitQfs supposed to be faster than RaBitQ? Did I miss some configs? Thanks.