> [Passing region indices] implies that all user code should be change to do the looping itself and be aware of region indices. 

Oh, and another thing, it could very well happen that there is but a single PVT (or saturation function) region, but that the end-point scaling options vary from one cell to the next.  That happens, for instance, in the case of Norne.  By explicitly requiring that the caller be aware of region indices, we're *also* implicitly requiring that the caller be aware of *all* (relevant) region mappings that happen to be active in a particular scenario.  I think that's the wrong trade-off.