Landscape: Add image overlay on top of terrain using real heightmap data

Is there to do this also for tiled landscape? I have a landscape with 4x4 tiles. I have the DEM and satellite image overlay exported as tiles with common names. While importing the tiled landscape one could provide tiled masks but not tiled textures. Am I missing something on this?

I read somewhere that for this a material instance need to be created for each tile and merged into the mastermaterial.

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But I dont quite understand how to do that. Any hints would be most welcome.