It depends.
If I was running out of space on my SSD and had slow internet, then I’d definitely put it on the HDD.
If I was running out of space on my SSD but had fast internet, I wouldn’t use any cache at all
Or realistically in my own situation, if I was running out of space on my SSD, I’d buy another SDD or replace the existing one with a larger capacity model. But this is coming from the guy with a pair of 1TB NVMe and a 4TB SATA SSDs in his system. I realize this isn’t a realistic solution for everyone.