Hello Dave,
I cultivate my Disas in 10 cm diameter and 10 cm in high plastic pots. Last year I start an experiment for some lager plants as my Disa chrysostachya in big coco-pots, where the plants grow very well.
Here are some pictures of my Disa sagittalis where currently are in Flower and the last pictures is an Disa chrysostachya bud where grow in a coco-pot. Near future I will send an pictures of the quite plant.
All the best,
Johannes