Ecosystems work as if you 'dropped' objects on your surface. I suspect it was easier to come up with a vertical drop above the horizontal plane of the ground instead of calculating the vertical direction across the whole surface of the object. You could create multiple spheres with ecosystems, turn their underlying material transparent (except for one) and superimpose them. Make sure to set the 'influenceof foreign objects' parameter to 0 when creating your ecosystems.

• agiel - www.linfa.net