Hclust2 --fperc value

Hi @fbeghini
I was using Hclust2.py script for making heatmaps, in the example given in github page GitHub - SegataLab/hclust2: Hclust2 is a handy tool for plotting heat-maps with several useful options to produce high quality figures that can be used in publication. they have used --fperc value 99. My question is that why have they used 99? I tried using different value, I made it 100 and then --ftop n was giving different species than it was giving with --fperc 99. So, what is the logic behind this? How should I select the correct --fperc value and what is the default --fperc value?

Thanks in Advance