Answering my own question - presumably that will make the leaf too small but that leads me to the bigger question - I don't really understand how you assess if the texture/distribution is correct when it's only mapped to a small sphere?
If I apply the current material to the background cyc (more like a ground plane/landscape) if looks terrible
ah ok... so the normal workflow would be to create the texture on the object you actually want to texture.... I know the last chapter is titled workflow but I've not got there yet