The units get warm, that is normal. The question is when is it too warm?

I would certainly not charge by induction (wireless) and then use it fully again straight away, because both disciplines lead to a lot of heat. But that applies to all mobile phones. Not in direct sunlight is the same.

Heat is poison for a long-lasting battery and a fully charged mobile phone should never be placed in the sun.

If you use the device a lot and do demanding things with it, then don't always charge it to 100 (more like 80%) and use it without a cover.

But back to the question. If the device is warm without you doing anything with it (not even charging) then check if a software is causing this (navi etc). The phone should not be warm when lying around. Everything else is harmless, as the devices measure their own temperature and switch off if necessary.

My model gets warm when I'm playing games or navigating but not much when I'm just surfing or messaging.

I have no problem with that