the only thing I could think is wrong is that the photoresistors are not the same values
maybe you should play around with the fudge factor , or the balancing factor.
What the fudge factor is is the amount of accpetable difference. Like say one photoresistor has a value of 12 and the other ahs 22 under the same light.
So a fudge factor of + - 10 will say if the values are within 10 from each other , they are considered equal , so 12 and 22 are considered the same.