We have observed law, and we have decisions being made underneath. Prior to the case, this looks like a straight-up trespass case. Under that plan, relative impact is decided by negotiation, but as numbers increase that's hard. So the court says OK, we'll make that decision, but we're limiting things to individual cases.
We're trying to make sense of observed law by understanding the institutional choices underlying it.
But the political process isn't monolithic, even if we're just talking about one of those alternatives: there's local vs. state-wide, or state vs. federal.
Whether something is internal or external is a function of participation. The Coase Theorem is really a statement about externalities: if transactions are costless then they will always solve the problems. The fact that they are not costless is the source of the problems.
The issues for market malfunction are transaction costs and benefits, speaking generally. It's non-zero transaction costs that make smoke in the atmosphere an externality, in other words.
Someone had to convince the court that they weren't dragging in all of economic due process, but once that was done, the court can reach the reasonable conclusion.