Hi Alberto,
You can use the Selection Tag and place either the same or an individual Random Filed in each.
Please have a look at these two versions:
https://www.amazon.com/clouddrive/share/yurnLdyV0SM01U9GOq3Eow5JoColVm7srMBBkcl5fhX
If you use the Random for each separately (…_01.c4d) then change the Seed Value for each.
In any case, the adjustment of the Fields Tolerance is crucial. Start by adjusting the most right-sided (Object Manager) and then the next to the left, to get the distribution you want.
A different effect can be achieved with a Vertex-map and the Vertex Shader.
All the best