The deep socket is fine by all accounts but there is not enough room for a spanner. A friend has changed the same sensor before but found it was set to far back for a spanner. i tested it in a 27mm socket and it was fine except it was too big

as for the sensor I was thinking this but what was said did make sense and Matt does know his stuff. His explaination was that the chip contains a different mapping that uses the sensor reading in a different way. It would appear the superchip mapping is much more reliant on the sensor than the norm. Obviously cant be sure its the problem but it would make sense as it gets better the hotter the engine is