Zimaboard 2 - kit nas - hdd temperature

Hi guys, a few months ago I bought a ZimaBoard 2 1664 Mini NAS kit.
I installed two 3.5" mechanical hard drives and installed Ubuntu Linux.
Everything works really well.

However, I noticed that the temperature of the hard drives (RAID 1) is a bit too high.
(around 52 degrees Celsius)

I already installed the fan on the board (as shown in the official video) that I found in the box, but it doesn’t seem sufficient.

Does anyone have any ideas on how to improve the situation?
Maybe the rack tray is too cramped and cannot move enough air?