Hi Bob, if you have floating grasses, they don't have anything to do with the fractal you use for distribution.
It's more likely that the populator doesn't have accurate information about the texture coordinates.
The first thing that springs to mind: do your populations "sit" on the last shader before the planet node? If not, please try this.
If they are still floating, you might need to compute the texture coordinates again before you feed the populator with it.
Regards,
Frank