operation behavior and non-additive roles

We ran into some unexpected behavior when moving into a Stabilization iteration, where users were able to deliver code without a review, despite the "Require Review" precondition being set up for the iteration. Looking closely at the Operation Behavior section in the Project area editor revealed this text:

An operation's preconditions and follow-up actions can be configured differently for each role. Note that operation configurations completely replace each other; they are not additive. The process runtime will choose the most appropriate operation configuration for the logged-in user and will use only the preconditions and follow-up actions defined in that configuration.

Our problem was that the "Require Review" precondition was only defined for the default 'everyone' role, since we assumed that the roles were additive. In practice, it looks like RTC is usually picking the 'committor' role that we set up, which had no preconditions defined.

So, a few questions:

A) Given a user with several roles defined in the team and project areas, how does RTC determine which role to use for any given operation?

B) To be safe, it seems like preconditions that we want to apply to every user must be applied to every possible role. Is there a way to duplicate/copy preconditions from one role to another? Is there a way to define a precondition template that will be applied if we create new roles in the future?

C) It appears that the non-additive nature was a design decision. Are there any plans to change this, perhaps to allow the team or project area to define the additive nature, or at least allow the global 'everyone' role to be additive with other roles?