It does not matter. Provided that the manufacturer of the flooring products (coverings, adhesives, etc.) says they are compatible with floor-heating systems (always defer to the floor-covering manufacturer’s instructions), the installation is UL-approved.
Installation of Mapeheat Membrane below luxury vinyl flooring follows the same installation method as engineered and laminate floors: First, embed the floor-heating system within cementitious material, ensuring in 1/4" (6 mm) of coverage above the heating system. Either a mortar or self-leveling compound can be used, but achieving the desired flatness is easiest with a self-leveling underlayment. Proceed with installing the floor covering on top, following the manufacturer’s instructions.