root size and repotting in s/h

[Becca]

Okay, one of my orchid seedlings (Hknsa. Sogo Doll "Little Angel" AM/OSROC) finally grew about 4 or so really good roots ranging in size from about 3/4 of an inch to an inch, which I had in sphagnum moss while regrowing its root system. I was told that if new roots on orchids are ever so slightly bumped that they will stop growing because they are fragile. So when I am converting a plant with new growth like this into s/h and I am filling the container with PrimeAgra, will the roots be damaged and stopped growing when the PrimeAgra is filling in around and over the root? It is pretty much impossible to keep the PrimeAgra from bumping the tip of the root, but yet it is recommended to convert a plant while it is in new growth so I am slightly confused on when the roots are not as fragile so I won't damage them?