By definition, if they are inter-cosmic - literally between world-systems - there is nowhere for them to live! A cosmos is a world-system - ours has Earth at the center surrounded by the orb of the heavenly stars and wandering planets. There is no world in the metakosmos/intermundia - it is literally "between" worlds... No planet, no stars, no world.
I certainly agree that the world, in Epicurean terms, is analogous to the modern idea of the "visible universe."
Would you agree that, although there is a finite about of matter and space in world-systems, there is an infinite amount of matter and space outside of (ie between) world-systems?