What's the formula for the FisherN normalization function?

I tried the FisherInverse Transform which is an Ehler function (defined in http://www.mesasoftware.com/papers/TheInverseFisherTransform.pdf) on the BandPass filter but that gives a much more defined curve (-0.1,0.1) range and doesn't require a 500 parameter.

Pl advise formula.. in essence, I'm not able to replicate the Z2 system.

thx
Kiran