Short interest isn't calculated by subtracting insiders & institutional from the float. Institutional does short stocks. So do insiders. ENRON ETC. They promote buying, while shorting themselves. They also promote shorting, while shorting themselves.
Short interest is calculated by dividing shares held short by the float. 3 mil short / 36 mil float = 8.3%
But if you look at the info in the link you provided, you will see they list short interest @ 10.8%.
Using 3.03 shares short and 28.06 float = .107982893799002 or 10.8%
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