Digging this up a little bit, but by the principle of how a hot wire MAF operates, it automatically compensates for increased pressure or temperature variations, as the cooling of the hot wire 'responds directly to air density' (not air volume). 

Was this train of thought that this particular MAF doesn't compensate for air temp mostly based off of
1. That you (julex) had lambda fluctuations (which seemed to be resolved with the FPR,
and
2. Because of the existence of an air temp output on the maf?   

I always thought that the air temp output on the HPX MAF was simply because with that particular make of Ford (and whatever else the HPX maf's are in) they decided to use a maf that combines the ambient air temp (or IAT) sensor together with the MAF sensor (just for an IAT or ambient sensor, not necessarily to correct an 'uncorrected' mass air flow value from the sensor).

Has anyone conclusively found out that the cars that use the HPX as the OEM sensor change the MAF reading value in the ECU based on the HPX's air temp output?  Or does that remain an assumption?

Edit: Just saw the title edit, so julex, your initial thoughts about the maf possibly not compensating for temp has been reversed since you found the cause of most of you lamda drift, or do you still speculate that the HPX doesn't compensate for temp (in addition to the FPR causing the drift)?

I recently reset FDVANS to all "1" to eliminate flow adjustments for temperature and that solved all of my issues with HPX and heat..