Shuttle's latest mini-PC has a 1.35 litre case, but it can still accommodate 65 W Socket AM4 processors. The XPC DA320 has dual-channel SODIMM RAM too and can power three displays at 4K.
https://www.notebookcheck.net/The-Shuttle-XPC-DA320-fits-65-W-Socket-AM4-processors-in-a-1-35-litre-case.515945.0.html