Doing short strangles around atm with the current options month series is high risk and needs to be traded high professionally. Stress is programed. You will need TA knowledge and not only knowledge about the option Greeks. If you suddenly find your self in a trending market, your fixed delta rules are out of question. So forget about it. Here only the break even points do/could lead the game. Very difficult task and most lose money at the end with it.
Consider the case of shorting May straddle. Once BEP (say at 6500) is reached, buy March 6500 CE costing 80. From then on what could go wrong? What better month to find out, than the "tides of March"