Question: Charcoal in potting mix for neps

[alpiner]

To all neps guru,
To increase media airiness for neps, I'm thinking of adding charcoal as one of components. Question is, what's the good size for charcoal bits (or not important) and relative quantity do you use in the mixture? Do you hv good recipee for bottom part of the pot?
I'm unsure whether I shd stick to perlite+sphagnum moss(~1:1) for bottom, and top 1" with pure dried sphagnum moss. Or add charcoal with SM, or charcoal/perlite/sm, ... Is it advisable to use charcoal for orchid, soaked overnight? Those are normally quite chunky. Of course, with brute force I can smash them left right center.
Materials that are readily available to me: SM, coco peat, perlite, charcoal. Your advice is very much appreciated. Thx in advance.