Right here goes......
there was a service bulletin (dated 01/03?) about irregular minimum level,which as far as i'm led to believe simply (simply

) required a later additive to be used.Although I dont have said bulletin to hand i'm sure (therefore probably wrong) you changed from DPX additive to Eolys additive (5litre tank which is mixed with main diesel tank fuel) which is made from cerium oxide solvent (thinners) hydrocarbon based so it lowers the particule combustion by 100oC.Therefore the particles burn off in the FAP at 550oC but this is now lowered to 450oC.
95% of the particulates are removed so when you 'wellie' the car you dont get the characteristic cloud of black smoke,applies to the 2.2 diesel engine).
The FAP is controlled by a seperate 'node' (non proxy-aligned) located behind drivers side dashboard....where else would it be

The filter itself has service life of 50,000 miles.When replaced the FAP must be reset by examiner.
The FAP under goes 'regeneration' which is dependent on exhaust gas temperature.There are 2 types of regeneration;
1)Natural-high temperature & fast driving or high loads which rises the temperature.
2)Artificial-coolant level over 60oC with engine load equal or greater than a preset level,will not take place at idle.
Regeneration therefore takes place when required as determined by the 'node' dependent of distance and fill up cycles which must be more than 7 litres