IIRC the Air Force delivers the situational awareness to the Army and Navy, and that the latter can build to fill any gaps they identify. We're now seeing that in effect via the Army and Navy's acquisitions (e.g., Army LY-80, Navy LY-80, etc) at the LoMADS level.The area of responsibility is defined by height and area. Army is responsible for air defense up to a certain altitude and the Air Force above that. Plus Air Force has primary ground defense responsibility around its bases. However, with induction of more long range SAMs with the Army this delineation might have become fuzzy but I am sure it is well defined. Army and Navy nodes feed into air force’s integrated air defense.
At this point the only question is who will own the long-range, high-altitude segment. However, I think they'll just extend the current approach (which seems to be working for LoMADS). In other words, each arm could end up with their own HiMADS, e.g., FD-2000 with the Army, a long-range SAM with the Navy, and another long-range SAM with the Air Force.