I agree with everything Gordon has offered. I would like to add that in my own collection, depending upon the particular plant and it's locale of origin, I also use pumice and/or orchid bark mixed with pure sphagnum or peat or sand. No vermiculite and only a little perlite.
It's not a good pic, but here's an example of VFT & the sphagnum I use. I can't base it on scientific fact, but I do think the sphagnum on top of the peat/sand/sphagnum/whatever mixture helps keep the roots & foliage cooler in the hot sun.
Of course the sphagnum can also strangle a plant so
that growth has to be kept under control, too. On the bright side, you can easily start & propagate your own sphagnum garden from thinning!
Think of it like a snake or any other herp. You want to replicate the plant's natural environment ... excess perlite or vermiculite just don't enter into that equation
