I also notice that the Acasis TBU405M1 enclosure is cool when the PC is awake (crystal disk info 32c) but very warm when the PC is sleeping (39c when checking right after waking)
The Realtek RTL9210 chipset generates very little heat, which is why it doesn't need a heatsink. A heatsink is often designed for the hard drive, even if it's a 10GB SSD, because the SSD itself gets hot. The one that gets hotter is the Asmedia ASM2464 chipset (40GB), which requires it to be placed directly next to the case's heatsink.
