It doesn't work like that. If there were 40 or 50 traders that actively short stocks they wouldn't all short and cover on the same day. Shorting would start one day and would be shorted by others until the chart tells them otherwise. A short could be continuous for many days drastically affecting the price. I would also contend that there are shorters that view their position as long, on the short side and hold on small bounces just as longs hold on short pullbacks.
If you know anything about shorting, you should know it drives down the price and many shorters will post anything to help that cause.
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