Importing heightmaps into individual LandscapeStreamingProxy

I’m in the process of importing a lot of topo data into Landscape tiles and I just figured out how the World Composition mode works. I can create new levels in the World Compositor and it expands my base Landscape tile. I can pick the individual LandscapeStreamingProxy actors and apply unique materials to each one. I can’t figure out how to load a heightmap into each individual tile. It appears that the Heightmap -> Import From File affects every tile, padding flat ground around the imported data. I have an area in excess of a hundred square miles to import and I want to maintain the 2 foot resolution of my source data. I originally started by slicing up the topo height maps into a grid and importing into multiple landscape objects, but I can’t paint across the seams with that process. It seems like the World Composition mode is great for those environments where the topo is created by artists in UE, but how do people deal with imported real world topo data at this kind of scale?