Different sensors probably. I'm pretty sure you should never run an O2 sensor pre-turbo.
Narrowband O2 sensors generally go just after the turbo near the top of the dump pipe. Wideband sensors usually need to be further down the pipe.
On the exhausts I've had made I've always had the ECU sensor about 15cm from the flange, and the wideband bung about 100cm from the flange. It's important not to run the wideband too close to the turbo, as it can overheat the sensor. Also make sure to mount it pointing down at least 10 degrees: