Your theory will only work for a small amount of the SI. At one point, there will not be enough shares sold short to manipulate the stock price.
My guess is that there is a shift into other (and perhaps more weaker) hands.
What if -let's say- 5, 6 million (or even more) shares sold short are shorted naked? What if the institution offering that amount of shares for shorting this stock, is aiming for a short squeeze itself?
What if they own already o couple of million shares 'long'?