We all have seen this pattern before. The price drops significantly, the comes back to where it dropped, stays there for a bit and drops again. I placed that trendline there because I believe we will see a quick touch there or over the trendline. I see 6400-6600 as a reversal zone but it's also possible to happen right now because the price is facing the 2018 support which is now resistance.
Overall, personally, if I would enter a short right now my SL would be large.