I think that's the look that gives the Chinese their distinction.  Because you can have epicanthic folds and it's kind of like a widespread EDAR trait but the wide forehead thing is pretty spectacular and not run of the mill.  And mind you not all Chinese have it but I would say Chinese are known for it.

I think the ranking of wide expansive forehead among Tang dynasty contenders might be something like this:

Chinese (Han, a particular Chinese type)
Tibetan (Another Chinese type)
Japanese (Related to Tibetan)
Central Asian (Connects to Tibetan on the western side)
Korean (I hear they might have a more potato shaped head which detracts from the expansive forehead shape)
Mongolian (Wide heads but not necessarily expansive forehead)