multiple roles issue - possible?

Hi
I have two roles, location and level if you like.

User A eg would be a "Bronze Subscriber" in "New Zealand"
User B eg would be a "Gold Subscriber" in "New Zealand"
User C eg would be a "Silver Subscriber" in "Australia"

I understand that permissions for multiple roles are "OR'd", however I need to be able to list documents so that:
User A can only see Bronze level docs with New Zealand category
User B can see all (bronze, silver and gold) New Zealand docs
User C can see Silver and bronze level docs with Australia category

Because of the "OR-ing" of permissions, that means User A can see a doc that is set for "Gold", "New Zealand" purely because it is a "New Zealand" category.

Can someone help me work around this please?