I mean you should be expecting a big loss, it's in the nature of the trade. Lot of little gains and a big loss. But if it has a positive expected value it's a good strategy. You like the opposite profile. A lot of small losers and an occasional big winner.
But what if the implied vol is already pricing in the move? Like how do you decide if the option is cheap enough for you to buy? Something I do with relatively good success is sell ATM SPX/QQQ/IWM calls and long the ATM call of the stock I think will outperform and vega weight them. Something you could maybe look into.
Sorry, was never good with option spread trading. I do better trading directionally and if I keep the losses small, profits will take care of themselves because they are larger. Big losses can come and it stings but, as long as I keep it to a minimum, overall, the results should still be good for me. My expectation is positive because I have a win % of 40%, loss % of 60%, average win is 2 times that of the losses. I do not worry about the option prices because I trade pullbacks, breakouts and reversals. Only thing I won't do is pay $1,000 for one contract. That would violate my risk management part of my trading plan. I have a $600 limit per trade most times. Options prices has been going down or flat most days before I enter the trade. It won't matter if I pay an extra $100 in premium if the stock runs up the following days after I enter the trade. The increased volatility will increase the option prices in a short period of time. Exactly, what options traders want!
.