Adam Warner tiene breve post sobre la mueca (skew) del VIX y la percepción de los cambios en el mismo (el VIX) desde el mercado de opciones.
The VIX uses a set formula based on the volatility of each qualifying SPX option. It normalizes to create a 30-day option, so it will incorporate the two nearest expiration cycles, up until the nearer one gets within eight days of expiration, at which time it leaves the calculation.
The next thing it does is weigh the options such that closer strikes carry more weight. And that’s where skew comes into play.
What I’m trying to say is that many of these VIX tweaks are simply mathematical. Skew is on the high side right now, so the effect is particularly pronounced at the moment. But for a guy simply trading SPX options and not caring about the VIX, he would not detect any change in volatility.