With the sensor in the plastic tube you will see differents raedh
The plastic tube work like a protect to sensor,and do not enclaved warm air,because the fan take all the warm air and go above it on the top.
But you will put the fan like photo,and for better put a aluminium tape all arount a plastic tube .The fan sucks air from the side of sensor out-temp -hum,and air flow go above on the roof
Of cοurse you must have the Stevenson screen at correct place,as i said before