I was looking at the outlier detection formula which uses the IQR and I wonder why it should be multiplied by 1.5? Can the constant be increased i.e 3 or 6 to be more "acid" if so under what criteria?
Certainly you can change the criterion.
The 1.5 multiplier is so that a certain proportion of the sample in a normal population will be outside it. But there is nothing sacred about it.
However, I would caution against any automatic method of selecting outliers.