E = mc2
The effects of the Heaters, as directed by those persons who are in command of the Control Center, are felt directly at various spots within the shell, mostly near the surface (there is no dispute that the Lattice Builders added this feature to make a Lattice World inhabitable though it might not orbit a star.) Likewise, objects, substances, and material created with the Mass Generators are manifested at areas definable in the Control Center. But where the Heaters and Mass Generators themselves might exist remains a mystery. It has been assumed for millennia that they have no physical presence in the Universe, and most likely exist in some sort of "other dimension" or "alternate plane."
The operation of the Heaters is extremely simple: how much energy to produce (subject to the output of the Power Films) and where to produce it, is easily specified at any computer Terminal within the World's Core. The operation of the Mass Generators, though, knows no limit of complexity; currently, on human Lattice Worlds, it is solely within the purview of the Terraformer-Shagrilizer Conglom.