Here’s relevant excerpt from V. Anandajoti’s 3rd jhana formula from Sanskrit work Arthaviniścayasūtram
experiencing happiness through the body,
Other than Ajahn Brahm (and his supporters), I don’t think anyone else in the EBT world in pali or agamas, or any other EBT school that I’m aware of, treat kaya as mental body. They all view the body as physical flesh and blood body in the 4 jhanas.
Even Ajahn Brahm’s beloved teacher, who he trained under for 9 years, the great Ajahn Chah, said body is physical.