The RB26 AFM's are rated less than the 25's I know that for certain, this is probably your issue... question though, is you AFM an RB26 one or 25? If you are using a modded 26 PFC with a 25AFM you shouldn't be having any problems
EDIT: Just saw you have a 32, no idea where the RB20 AFM's fall in the scheme of things, would think the 26 has a greater reading range however