Leslie, the masdevallia species we grow is potted in a small bark and charcoal mix. We grow it root bound as it appears to like being tightly packed into its pot. We also grow it in the coolest spot in the greenhouse with very high humidity and lots of air movement. It gets fed and watered on schedule with everything else in the greenhouse. (Too many plants to be specific to one or two orchids.. lol)
I hope this helps. Here is a photo of our masdevallia. It is about 16 years old now, has won several blue ribbons at orchid shows, and has been growing in this same container for at least 10 or more years.
Masd. Pixie Shadow (infracta x schroderana)