There will be a Reynolds number effect, which I find it difficult to apply with a penetration coefficient. I've been into this dilemma and I found A/ that some suppliers of perforated panels have ready-made 3D CAD-models available for customers, and B/ some CFD software have a set of perforations and/or nets built in. Unfortunately it was a couple of years ago, and I did not archive the info, but it was pretty easy to find on the net.