Hi,
Where have you got the sensors situated with respect to the fan/s?
You only need to use one sensor and configure it like a pitot tube that aircraft use to measure air speed.
Just put a tube on the inlet of the sensor and point it at the airflow coming from the fan, a very small diameter tube/pipe would be needed for such a sensitive device.
You could even calibrate it for air speed.
Just a thought, and it would give you greater separation of readings.
OR a flap in the air flow of the fan, and a switch or potentiometer measuring angle.
Tom... 