The histogram shows the distribution of Boundary Likelihood Values (BLVs) for the dataset and the threshold you set. This histogram appears as if the threshold includes most of the BLVs in the dataset. In part, this is a problem with the histogram visualization. To improve this, we will need to change the formatting of the histogram.
We will change the number of bins to display the data. The problem with this dataset is that most of the values are in the smallest bin, close to zero. So we will increase the number of bins displayed to improve the view.
Right click in the histogram window and choose "Properties."
Select the Bars tab of the dialog.
Choose 50 bins (the maximum).
This will improve the display. Remember the BMV cutoff is the top 20% of all BLVs, so 80% of the BLVs are below the threshold (illustrated as a slim red line). Most of the BLVs in the dataset are close to zero, which you can see in the table or map.