Hi Lluis,
sorry but unfortunately I had not too much time lately, so I couldn't go ahead in that project. Anyway...
I don't have any chance of moving that sensor in another location. The board is very small (20x24mm), and in one side (the whole side!) there is the radio, and in the other side other components (mcu, resistors etc..), before posting I had already confined the sensor in the corner of the board, but that was not enough. The only thing I can actually change is the removal of a small PCB copper plane under the sensor as AN892 suggests, hoping that the major thermal disspiation actually happens in other places. Conversely, the only thing I can do is duty cycle the radio, having then hard time for the radio protocol and communications...... I hope to fix the board in next week, then ordering them again (it will take about a month to arrive ouch!).
The AN892 document you pointed me at is very valuable.
Thanks,
Natale.