Leo, this detailed information is so useful. Perhaps it should be added that Sinningia tubiflora is a native of my country, Argentina, where it grows in a practically subtropical region, receiving year round rainfall. Yes, it grows in a porous red soil in meadows in full sun. The plants are dormant leafless in winter and sprout in spring. Flowering starts in late spring and last a couple of months. It is always in full sun and the tubers are some 4 in/10 cm. deep. If tubers offset rapidly (which to me is a sign of the plants feeling unwell) put them in several separate pots: when tubers completely fill the container losses to rots are lethal.