by chance i think i fixed the problem by myself.
i was reviewing RSD policy again, and checking the prod guide.
as shown below , in the communication tab i changed from 5 to 10min the fist two fileds
then i selected "use local sensor election" and "All sensor active" as somehow suggested in the guide.
even if these changes seems not having anything in relation with the OUIs exclusion, the fact is that now the exclusion is working....
not sure if you have an explanation for this, but anyway...