Whenever I try to create a credit spread on IBKR it shows spx delta which is considerably less than the delta of the individual short strike. From what I know delta is basically the chances of the short strike becoming current strike price. My question is when people say delta should be around or less than 10 (depending on your risk taking capability) do they talk about the short strike delta or the spx delta that I see when I create the spread and what's the difference between the two