Firstly I don't know why you consider January to be the benchmark price? Just because it's the first graph DCE displays?
All week you have been posting graphs of the September contract until today. What do you think changed on the 4th August (quite a random day)?
Next you will note for every other commodity traded on the DCE that the first contract they quote is always the most active contract, most of which is still the September contract.
You can convince yourself of that here: http://www.dce.com.cn/DCE/Market_Data/Market%20Statistics/index.html
But in any event, if you want to go quoting Y712.5 as the current IO price compared to Y772 (JUST an 8.5% difference), well that's on you.
(20min delay)