Most of you - shoosh if you don't know. Serious. Don't give advice if you don't know WTF you are talking about.
Any wideband should be no closer than 6" in distance to the turbo exhaust. Even then, most mfg's suggest 24" away from the turbo exit. This is due to the possible extreme heat - it will litterally cook the o2 sensor.
A couple people said it - the test pipe - is a great location for the o2 sensor.
Readings will be good, and its in a "cool" environment. You need only to worry about it being kicked by road debris (rock, speedbump etc)