Try to fit the type/size of roots to the media you plant them in. Even with Leca, there are two sizes or more. I use the small clay pellots (1/4 inch or size of peas) for oncidiums (which is the family your plant is in wether it is a colmanara or a sharry baby), and larger, marble size clay pellots for catts, phals and other thick rooted orchids. You could use small bark pieces mixed with pearlite and small sphag bits. th sphag will hold a bit of water for the roots, while the small bark bits and pearlite allow some air to the roots.