It's changed since they've implemented the new Chinese only lanes. I used to use the area on the left you are describing but that has been totally removed. I wandered over to the diplomat area on the right (no signage for TG J but they processed me anyway). I figure there has to be a formal area now but no idea where.
The departure fast track is wonderful but TG have always been terrible at communicating inbound fast track facilities. Actually led me to book 2 X SQ J tix so I don't have to faff around on arrival and they were marginally cheaper anyway.