hey brassa, your mix sounds very good.
I was just reading this article about cymbidiums but the info I think is relevant for most orchids in general.
It explained charcoal in great detail which I need to add to mine in future.
The 8 Best Potting Media for Cymbidium Orchids - Orchideria
The article is nearly complete but reading through it it feels like towards the end the info starts to trail off, giving all the pros and cons of barks, mosses but then falls short on the hydroponic media lumping pumice and lava rock and even clay pebbles as one and the same media and that is like lumping redwood bark and charcoal as the same media which is very innaccurate so apart from the serious lack of detail on the alternative substrates to use towards the end the beginning is very useful I found.
I have also come to find that pumice can come in all sorts of different grades, some only holding 10% of water, others holding 30% water, sizes make a big difference in how fast the pumice will dry so there is no perfect mix but knowing the different properties helps pick what works best.