But the highest OI will be 1600. Now see the premium of 1600. So the guys who will sell March 1600 will be unaffected to even 1640 levels. If that reaches I will not close (if I am talking about me, I don't follow stop losses much in many cases.) I will hedge with 1600PE.
But 1620 if breached upside (So, yes, 1623 looks like fine SL) then it won't fall sharply (rather consolidate). Book the trade and sell ATM CE. That will shift the BEP to 1640s :)