So your argument is simply that we were using the wrong terms, calling everything head pressure where as theres two different concepts: head pressure and flow restriction. Like the way everyone calls all sea slugs nudibranches... Never mind then.
I blame Delbeek and Sprung for mixing me up. "Head pressure refers not only to the vertical distance a pump must push the water, but also any resistance to flow created by pipes, fittings, and valves." The Reef Aquarium Vol 3