There are several ways, geographically, culturally, administratively, to define which provinces belong to which regions...Thins is a commonly-used way of China's 7 regions: http://www.ziyexing.com/files-7/geography/Geography_inf_13.htm …. But no matter which way, Sichuan is generally considered a part of NW China.https://twitter.com/kchangnyt/status/1071184425206104064 …
Don’t mean to be combative. If you were writing about Ohio for a Chinese audience, would you say it’s in the Midwest? It’s nowhere near the western half & it’s on the northern border. Wouldn’t it be more informative to say it’s in the eastern central part of the U.S.?