Jack:I am a little bit surprised that SPY starts the cycle below the index though. So how can that be explained?.... Let me think about this for a few minutes...
I do NOT use the SPX spot price in any of my option pricing or greeks, but derive the forward price instead from the option chains. (This way I can simplify the handling of dividends for my SPX greeks) This is working great for me. Since you can't directly trade SPX, and precise greeks using SPX spot is awkward at best, it may find few, if any, places where the use of the value is critical!
