I expect this makes the chassis around the CPU/heatsink get relatively warm; I'm not sure how these things are designed but I think in this instance the case itself is part of the cooling solution dissipating the heat.
Therefore if it weren't getting warm, there could be a problem...
Check the CPU temperature with something like HWinfo. Could be worth checking the HDD temps too, in case the CPU is warming that up too much. If you're not sure what 'good' temps for the hardware are, post what you see here and people can advise.
Actually I've just found a review of (a slightly older model of?) that chassis with some thermal images:
20 and 40 WAlong with low power consumption chips, silent computers are also expanding. The British company Akasa has been specializing in the development of cases optimal for this purpose for the last few years. We have put their most progressive model through editorial hell. After exploring...
www.hwcooling.net
Note that the orientation affects temps.
The review shows that the components were generally at their coolest with the PC oriented "vertically, in width" (as they describe it), while the chassis was very warm. Whereas orienting the system differently could result in increased temps for the components, with varying effects on the temperature of the PC to the touch.
Unless you're holding the thing all day long, you probably want to favour whatever arrangement helps minimise the heat for the components, even if the case is a bit warmer as a result. As long as you're not hurting yourself touching it ofc.
Orienting the case differently may help a bit. But that article does suggest it gets fairly warm, presumably by design.
As above, check the temps of the components inside to make sure that the PC is warm because it's transferring the heat away from the components sufficiently, rather than warm because it's just cooking itself