Combining Algorithms & the Hierarchical Resource profile

All, I see no reference to a combining algorithm (CA) in the Hierarchical Resource profile.
Are policy writers expected to use the core CAs, or are they expected to write their own CAs specific to this profile?
I expected there to be some CA that gives precedence to rules that match lower in the tree.
For example, given the following tree of resources: A +-- B +-- C +-- D And two rules that target resource-ancestor at A and D, respectively, I expected the one at D to take precedence for a request with resource-id=D, but I can find nothing in the profile that actually makes that happen.
Am I missing something?
Thanks, Ray