Well, generally the failure occurs around 50% of the Height. This time since the Height was 32, and the 2nd bottom was at 678, the Failure was expected around 678 + (32/2)= 694
The SPX overshot it quite a bit, but still it was I think below 70%. The best is if the failure occurs in the 40-60% zone.
I would say if it reaches 80% of the Height, it won't fail at that price.
Edit: We just hit 672.5 which is getting pretty close to the 667 predicted 3rd bottom