70 percent Zebra setting doesn't show up even when image is bright

[offbeatbryce]

I have a Canon XA10 and the Zebra setting is set to 70 percent. There are only two options, 70 and 100. The camera has a built in Waveform monitor and when the Waveform reads 90 IRE The image is obviously just a bit to bright as the wall it washed out. The Zebras don't even show up on the face of the person I'm filming. Does anyone know why?