What I have observed is that at magical number 70l, bulls or bears are confident of holding that level. Only issue is at that OI most of premium is already squeezed out, so you are playing with 25-35 and with a 20 point stop loss it's only a 1:1 RR, instead best way is to play with trend and buy near strike level or sell when spot is near strike level, last time when nifty dipped to 7584, it gave RR of 1:4