> That does however mean that we can't pass the region index into the functions that compute saturation-dependent quantities. In general those calculators need the actual cell index, whether the end-point values are given by cell or by depth.

You're right. But (after miscommunicating for a while) I thought that the consensus currently is that the higher level classes like `Blackoil*` take cell indices, while the low-level `Pvt*` ones take region indices?