Shortfall Risk

If given a a 95% or 99% confidence interval instruction in a portfolio selection question (choose among best portfolio) along with a minimum return requirement (portfolio can’t lose more than 5%) we would use the formula: Portfolio Value (Return - standard deviation*(1.65 or 2.33)) and see if this is more or less than the -5%. If not given a level of confidence do we just use Portfolio Value - sd*2 ?

Is this just a given formula?

That’s exactly how I would answer the question.