o2 sensor not switching

I have been working on getting a 2002 ws6 tuned properly. But the o2 sensor graphs look much like the logs at 6:50 in the worked example on the practical reflash module. Can anyone elaborate on when the o2s go flat if its a sensitivity issue in the tune or an actual o2 sensor problem?

Can you link to the specific video that you're referencing? I'm only guessing here but the narrow band sensors used in the worked example are only useful at a target of 14.7:1 / Lambda 1.00 so this is the only area they will show activity. At WOT they will flat line at a voltage around 0.9 or thereabouts. If that's what you're referring to then this is normal narrowband O2 behaviour.