I have almost all multifloral species and I don't grow anything else. They like CHC, fine bark and perlite. CHC holds the water very well so your problem could be solved using it at 30%. There are some special variations for the following plants: Anitum: add sphagnum and keep the mix wet all the time and NEVER let it dry out. Adductums: little bit drier than anitum. Sanderianum: add coco husk fibre (yes, only the hairy stuff) at 10%. Ooii: is pretty easy to grow and likes a little bit more CHC up to 50%. Randsiis are doing well with a little bit more CHC and sphagnum addition. Wilhelminaes have very thin roots and they should get small bark and small CHC (i shred it before use because small CHC is not available here).