Wideband in tailpipe

[Niall]

To be fair I wouldn't know what's inside the MOT station testing box.
It could be a standard WB sensor for all I know or they could use a different detection method.
But If I recall the other day getting my MOT it fannied about for a bit (warming up??) then did a free air sample, before being stuck in the exhaust pipe.
Similar to my LM-1 doing a free air at inital startup for getting a reference.

Since WBO2's have a heater built in to get the sensor up to working temp the distance doesn't matter in so far as the exhaust loosing temperature as it's the element that will regulate it at the operational temperature. So distance from the exhaust ports in terms of temperature of the gas isn't really a problem.

Wrong wrong wrong

Lambda heaters do not get them to their optimum working temperature. They aid in getting them close quicker than the exhaust gases can. Quicker the sensor is up to working temp, quicker it can be active and helping with emissions.

A Lambda sensor WILL NOT work correctly in the tail pipe. It will give a reading but the accuracy will drop big time. A lambda sensor is nothing like a gas analyser in a garage.
The sensor needs to be as close to the collector as possible to get an accurate reading. Anything else and i wouldn't rely on it. Also, its going to be after the cat then as well. You want the reading before the cat.