Huh? 20% down move on SPY... 155 from here. What is 1-2% referring to?
We are guessing how much / how fast would SPY have to move to see a 100% increase in VXX.. not guessing how much SPY WILL move.
Can't say for sure... depends upon the "degree/conviction of fear" psychology at the time. However, a 20%-ish drop in the SPY in 2011 produced about a 200% rise in the the VXX.