Are those push or pull fans? I would expect them to be the other way round pushing the hot air away from the boards?
Pull, sucking the hot air from radiator and pushing them away from the board.
The voltage reported by cgminer comes from some on-die sensors, so it will always be lower than the setpoint measured by the VRM, which happens off-chip. That's normal.
Do you still have that piece of MDF right behind the boards, and is there any air flowing over the boards themselves? You can see similar things if the VRMs shut down due to high temperatures.
Right, I'll try more air flow over and under the boards. I have ~50cm standoffs which the boards mount on so there's space below the boards for airflow, just need to attached fans to my frame.
Will report back once i've made completed the build.
Cheers,
QG