I don't want to raise the bar unnecessarily high, but Chuwi should not "think something", you have to know for sure, because it's your devices.
Why would a tablet being charged facing down bad? If the internal components are not resting on the screen, then what's the difference in the internal space? Wouldn't heat dissipate from the bare back of Chuwi device literal surface the best anyway? What does gravity do in that position that is bad for screen while charging? It's not a guessing game please.
I'm not that well informed compared to others, but my questions and demand sounds very reasonable to me.
Fwiw, I charge it in portrayed mode with the back leaning against something like in my folded legs, or while on a tablet stand in portrait mode. With the essentials recommended aukey charger and cable.