A bit of an odd question. I looked on the S4-mini purchase page and product page and I can't seem to find what is the exact amount of mm in z-height for an SSD that it can fit (with a gigabyte 1070mini installed too).
Im considering if I can fit 2x 2.5inch laptop SSHDs on the SSD bracket, they are
2TB Seagate Firecuda's that are 7mm tall.
BUT, can i fit a 9.5mm or 15mm tall 2.5 inch laptop HDD too?
The official answer is 7mm drives are compatible.
The unofficial
enthusiast at your own risk answer is It depends on alot of things--how you install the card, ribbon cable, some cards aren't perfectly square and sit higher toward the front of the chassis...
With my new ribbon cable I would say you probably could fit 9mm drives with clearance...maybe even a 15mm laptop drive with plastic backing in
some installs ( like this 1050ti build I have sitting in front of me).
As far as HEAT goes....the back of the 1070 MINI gets to be outrageously hot. It doesn't throttle or anything, but I think it would cook a spinning drive. With drives over it, I'm not sure. I wouldn't recommend it, but would I try it as a enthusiast? If I had a need sure.
Hope this was a little helpful...