You should still have a free passage of air,and it seems to me that this is not the case,
and the question is how much HDD contributes to the temperature.
(And it depends on the type of HDD)
I do not think I saw it in my box, 80 C.
True, these processors can have a high temperature ,but 80 c is high.
Put the box outside and measure the temperature.
The HDD is a normal 2.5" drive (it is not a SSD) i had the epg cache on it but i doubt that is the source of the heating.
I figured out why i had 80C... it where because my XBOX ONE is under the STB and when it were working it where heating the plate under the box.
However still on 4K channel temp rises to about 74C. If i have PIP in progress it becomes 76C on moments.
If i watching SD channel now it is 67C. On standby it drops to 62C.
Ofcource all that readings are when the box is in that place under TV and the value comes from the internal sensor (drivers?). I do not have yet external thermometer so to get more accurate values.
But i will get one. I heard that that ARM CPUs can work even on 100C. What i worry about is that some other components can suffer from that temps (like condensators in tuner). What i noticed is that most of the heat seems to come from the tuner compartment the box cover plate just above the heat-sink is not so hot compared to the place above the tuner. But the bottom place of the box seems a bit hot just below the CPU (well on hot i mean i can hold my hand with no problems but is warm)
@Matrix10 - For comparison what are your temperatures?