I consider the bitUSD market about normalized as of the time of this writing. If it stays permanently that way remains to be seen!!!!
Any way here is the meat of why bitUSD cannot trade with 10% premium and... bitCNY stay about 1:1 to CNY.
a. If any disparity between those 2 (bitUSD and bitCNY) do exist bitCNY shold trade with more premium than bitUSD as it has more utility. bitCNY has 2 ramps to CNY. Even the CNY itself is arguable more useful as currency as far as BTS products and the token itself is concerned - because the leading BTS exchanges has far more pairs BTS/CNY and CNY/whatever crypto; while bitUSD as well as USD itself is in no trading pair on virtualy any of them.
b. aside from point (a.) which is more or less gravy on top of the fundamental point. bitUSD and bitCNY should be pegged to each other the same way the CNY and USD are pegged. If nothing more (and there should be more) the feed prices of bitCNY and bitUSD should be relatively tightly pegged.
Based on b. above - here is a trading strategy to profit from unreasonable bitUSD bulls and stop their madness:
- Short bitUSD when its premium over the feed goes too high.
- Buy bitCNY for the same value as the bitUSD sold (i.e. about 6.19-6.21 bitCNY per bitUSD).
*How much is too much disparity between bitUSD and bitCNY premiums? It is up to anybody's judgment, sentiment risk aversion and greed

My personal opinion on this matter is of no consequence, but I do believe if any dispairity do exist it should be in favour of bitCNY being more expensive (per point a. above)
* Practical example - if you can sell bitUSD say 7% above the feed and buy bitCNY at 0.5% above the feed. - this is give or take 6.5% arbitrage opportunity; If you do this with small amount of your total BTS - say 5-7% you have practically guaranteed this 6.5% return; you have a lot of BTS left to re-short even if the price of BTS goes way way down.
* It is very important to realize that you are not really short bitUSD.... your long bitCNY will offsets your short bitUSD (so you will win about exactly the same amount from it as you lose from the short bitUSD - if the BTS price goes down)
Enjoy trading and do not let those bitUSD bulls go too crazy...and if they do just take their money!