I think , the normal distribution takes a sum of risk free interest rate and vol^2Henced1 = NormSDist((Log(frw / strike) + (0.5 * Vol^ 2) * T) / (Vol* T^ 0.5))should bed1 = NormSDist((Log(frw / strike) + (rate + 0.5 * Vol^ 2) * T) / (Vol* T^ 0.5))

I guess vega of the Tarn will be at peak as it nears the big figure , making the knock in/out more probable. But it also depends on how much the big figure has accumulated and how the leverage is going to be positively benficial. Can somebody throw some light on this