So… Few very subtle barely visible differences… Not sure if you are going to notice at all… Spheres are probably a good approximation.
I don’t really see much changing in GI in the shadows. Might not be the best scene for it, but, hopefully a full shader is not that important and the facing angle tricks possible with current Diffuse BSDF might be good enough to replicate this in Cycles without trillions of instances. it’s still not clear how common these effects are in real materials. … but to be honest from my experience at making shaders from reference, I suspect there might be some common materials with this… I think various fabrics may have these quite often and understanding this better might actually be of help for creating shaders.