good question(s), Preston.
one thing that I noted and took for granted was the assumption of certain standards: natural gas pipe, for instance - compostion and construction between europe and north america and probably the rest of the world may be slightly different, but not enough to matter enough. You're probably asking about water in PEX vs Copper pipes, or gasoline in the vinyl/plastic vs rubber (or aluminum) fuel lines.
Study up on Inductors and their magnetic fields...YouTube and wiki and your search engine of choice (I like DuckDuckGo) will lead you to wonderful places.
this bifilar inductor coil concentrates the field, and oppositional forces to the direction of flow through it are I suspect mitigated by the aligning tendences the field presents to the medium passing through the envelope to enough of an extent that systemic efficiencies can be realized. (wow, the coffee's working very well today...)
there's a degree of faith to this, but there's also evidence. if you're willing to experiment (and learn what to vary in your own experimentation), you'll eventually hit on the solution to YOUR equation. Or not, and you will have learned some things from trying.
In my case, simply with the one coil on my fuel line, I'm seeing steady mileage while the weather gets colder - that's not normal (it usually declines). I'm going to add another coil to my fuel line closer to the filter (rather than at the engine) and see if that continues/improves - I have to get underneath the car this weekend to change the oil.