A sell is a sell is a sell - it doesn't matter whether it's from a short or an insider. It's just the basic instantaneous supply vs. demand and that is a fact! It drops the price down at the moment it goes to market. Too many of these insider sells are made in large blocks. I have seen them come up and the short sellers have used them as a trigger and pile into it. Now, it's another thing to say what really matters in the long run.
But for the short run, if you want to find out then sell 1000 shares into the bid. And if anybody really wants to make up for insider sells, then they should buy a block of at least 10,000 shares at the ask. See what that does.