thanks for those links - I did have a look at those and checked relevant parts of the server/publisher reference guide once againt - but still have no solution yet.
To me it seems that it is not possible to Loop&Reduce (=produce several smaller versions of one source document) and then assign users/groups to each individual smaller version UNLESS I have a field in the data model that would specify the users or user groups that have access?
This still isn't clear to me.
I believe what I am trying to do is a very basic case: loop&reduce the source docuemnt (i.e. one copy for each region) and then restrict access for each copy in a way that users of a specific region can only see the copy of their region in access point!?!