Logistic regression threshold value
So there two ways of doing this, IMHO, 


By creating a well balanced target variable by choosing the right threshold. As I suggested in the comments above. In doing so we are simply taking care of values which should be treated as positive which would otherwise become negative if we take lower threshold. 
By using the mean threshold and that will generate imbalanced target variable and when you perform the modelling, you can see the ROC and PRC curves and decide the threshold based on that. But keep in mind, it also depends what kind of problem you are solving.