Yes, I discovered that ages ago… Transcode folder, yes, if you have it set correctly manually it will use the external location… but Plex completely ignores your choice of external storage for the cache folder which is ridiculous on a device like Shield TV with such small internal storage. Not to mention it’s flash storage that probably doesn’t have great write endurance and can’t be replaced so I live with the knowledge knowing that Plex is slowly killing my Shield TV.
They seemed disinterested in treating this like a serious problem warranting fixing, and seem to have been focusing on the retro games functionality that nobody asked for and nobody wants instead. 