The difference between your two afms does seem kind of far a part and 0.2-0.5v is definitely too low for crusing voltage.....should be around 1v.
To tell you the truth I had the same problem with my pfc as well, where it would get lean if left sitting while hot. Thing is water temp never rose, only air temp by a few degrees, and as normal with any ecu, fuel is added with an increase in temp but the pfc showed exactly the opposite!.......I also had the O2 feedback off so that also ruled out a bad O2 sensor......so I just gave up after a while and let it do its own thing ,as i never had reason to have it parked stationary for so long where the afrs would have become dangerously lean anyway.
Also I had no misfires or anything out of the ordinary otherwise....well except for that common dead spot that I described before and which nearly everyone else has experienced..... This was on stock inj and afms too btw.