I tried to search on Google but you can only find PCB temp for this unit.
Also tried to search for the BM1397 datasheet but no one share it yet.

I think the Asic chip max temp for the 17 series is usually around 110c-135c.

My suggestion is better run it in auto mode instead of running it in manual mode because if you set it near the max temp you just likely frying your chips to death.
And it is always better to keep them cool.